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>

certbot-dns-rfc2136/setup.py

@@ -17,14 +17,16 @@ install_requires = [
     'zope.interface',
 ]
 
-if not os.environ.get('EXCLUDE_CERTBOT_DEPS'):
+if not os.environ.get('SNAP_BUILD'):
     install_requires.extend([
         'acme>=0.29.0',
         'certbot>=1.1.0',
     ])
 elif 'bdist_wheel' in sys.argv[1:]:
-    raise RuntimeError('Unset EXCLUDE_CERTBOT_DEPS when building wheels '
+    raise RuntimeError('Unset SNAP_BUILD when building wheels '
                        'to include certbot dependencies.')
+if os.environ.get('SNAP_BUILD'):
+    install_requires.append('packaging')
 
 setuptools_known_environment_markers = (LooseVersion(setuptools_version) >= LooseVersion('36.2'))
 if setuptools_known_environment_markers: