Make externally snapped plugin updates more stable (#8145)

Fixes #7863.

Connect command is `sudo snap connect certbot-dns-dnsimple:certbot-metadata certbot:certbot-metadata`
Logs are `cat /var/snap/certbot-dns-dnsimple/current/debuglog`
Echos in hook are only printed to terminal when it exits 0; otherwise, check logs in `debuglog` mentioned above.

Manual tests include all iterations of connected, unconnected, installed for the first, second time, etc, with passing and failing version checks.

* Make dnsimple not update if certbot is too old

* create an interface to read cb version

* add missing newline

* fix syntax

* trying to figure out the consumer syntax

* trying to figure out the consumer syntax, again

* only check post first install

* valid setting name

* test for first install differently

* snapctl doesn't error if it fails I guess

* time to do some print debugging

* continue playing with syntax

* once again, fooled by bash int vs string comparisons!

* debugging

* if we use post and pre together we can do this

* is this how content interface syntax works

* it's a directory?

* more debug

* what's that error message again?

* try other syntax

* if it's not documented just guess at syntax

* actually, I think this is the syntax

* oops didn't set for new hook

* test passing information along connection

* interface attributes can only be set during the execution of prepare hooks

* just do it with main connection

* undo last few test changes

* Add some printing to make sure we understand what's going on

* create empty directory to bind to

* put mkdir in the correct part

* let's inspect the environment

* it can't run bash directly.

* perhaps only directories can be shared via the contente interface

* update name of folder

* echo to debug log to understand what's going on exactly. we have file access though!

* update grep for new file

* more printing

* echo to the debug log

* ok NOW all print statements are going to the log

* why does echo need two >s

* remove unnecessary extra check, just check if the init file is available

* check if certbot version will be available post-refresh after all

* pre-refresh hook is not necessary to get certbot version

* update mkdir so we don't have to clean each time

* try comparing version numbers in python

* it's python3

* we need different prints for if we succeed or if we fail.

* improve bash syntax

* remove some debugging code

* Remove debug script

* remove spaces for clarity

* consolidate parts and remove more test code

* s/certbot-version/certbot-metadata/g

* use sys.exit instead of exit

* find and save certbot version on the certbot side

* change presence test to new file

* switch to using packaging.version.parse instead of LooseVersion

* switch to requiring certbot version >= plugin version

* add plugin snap changes to generate script

* Add comment to generation file saying not to edit generated files manually

* Create post-refresh hook for all plugins with script

* generate files using new script

* update snapcraft.yaml files for plugins

* bin/sh comes first

* Add packaging to install_requires

* Check that refresh is allowed in integration test

* switch plug and slot names in integration test

* Update tools/generate_dnsplugins_postrefreshhook.sh

Co-authored-by: Brad Warren <bmw@users.noreply.github.com>

* small bash fixes

* Update snap readme with new instructions

* Run tools/generate_dnsplugins_postrefreshhook.sh

* Update tools/snap/generate_dnsplugins_postrefreshhook.sh

Co-authored-by: Brad Warren <bmw@users.noreply.github.com>

Co-authored-by: Brad Warren <bmw@users.noreply.github.com>

tools/snap/generate_dnsplugins_postrefreshhook.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+# Generate the hooks/post-refresh file for all DNS plugins
+set -eu
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+CERTBOT_DIR="$(dirname "$(dirname "${DIR}")")"
+
+for PLUGIN_PATH in "${CERTBOT_DIR}"/certbot-dns-*; do
+  PLUGIN=$(basename "${PLUGIN_PATH}")
+  mkdir -p "${PLUGIN_PATH}/snap/hooks"
+  cat <<EOF > "${PLUGIN_PATH}/snap/hooks/post-refresh"
+#!/bin/sh -e
+# This file is generated by tools/generate_dnsplugins_postrefreshhook.sh and should not be edited manually.
+
+# get certbot version
+if [ ! -f "\$SNAP/certbot-shared/certbot-version.txt" ]; then
+  echo "No certbot version available; not doing version comparison check" >> "\$SNAP_DATA/debuglog"
+  exit 0
+fi
+cb_installed=\$(cat \$SNAP/certbot-shared/certbot-version.txt)
+
+# get required certbot version for plugin. certbot version must be at least the plugin's
+# version. note that this is not the required version in setup.py, but the version number itself.
+cb_required=\$(grep -oP "version = '\K.*(?=')" \$SNAP/setup.py)
+
+
+\$SNAP/bin/python3 -c "import sys; from packaging import version; sys.exit(1) if\
+  version.parse('\$cb_installed') < version.parse('\$cb_required') else sys.exit(0)" || exit_code=\$?
+if [ "\$exit_code" -eq 1 ]; then
+  echo "Certbot is version \$cb_installed but needs to be at least \$cb_required before" \\
+    "this plugin can be updated; will try again on next refresh."
+  exit 1
+fi
+EOF
+done