Correct certbot-auto for Fedora 29+ (#6812)

Fixes #6698

Fedora maintainers engaged a deprecation path for Python 2.x with Fedora 29. As a first step, python2-virtualenv does not install the virtualenv binary anymore, in favor of python3-virtualenv, and so the installation of Python 3 virtual environments by default.

However, certbot-auto installs python2-virtualenv for all recent RPM distributions, and relies of the execution of virtualenv, and this is failing the process.

Since the plan in the future is to remove Python 2.x from Fedora, this PR follows this logic to fix certbot-auto: started to Fedora 29, certbot-auto will install and execute certbot on Python 3. This implies to detect that we are on Fedora 29+, install python3-virtualenv that will install also Python 3 dependencies and virtualenv binary, then instruct the process to use Python 3. This is in fact similar to EOL distributions shipping with Python 2.6, and for which Python 3.4 from EPEL is installed and used.

Older versions of Fedora continue to use Python 2.x, and their process is untouched. Four scenarios are covered here:

fresh Fedora 28: old process is used, nothing changes
fresh Fedora 29: new process is used, Python 3 is installed, certbot runs on it
update Fedora 29 from 28, already installed certbot-auto without rebootstrapping required: existing venv continue to be used, certbot runs on it
update Fedora 29 from 28, already installed certbot-auto with rebootstrapping required: new process is used, installing python3-virtualenv, python3-devel and python3-rpm-macros, Python 3 is installed, certbot runs on it

* Add a step to handle python3 on fedora29

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: adferrand <adferrand@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: adferrand <adferrand@users.noreply.github.com>

* Update letsencrypt-auto-source/letsencrypt-auto.template

Co-Authored-By: adferrand <adferrand@users.noreply.github.com>

* Update rpm_python3.sh

* Rebuild certbot-auto

* Empty commit to relaunch CI pipeline

* Add changelog

* Update CHANGELOG.md

Co-Authored-By: adferrand <adferrand@users.noreply.github.com>

* Update CHANGELOG.md

CHANGELOG.md

@@ -6,7 +6,8 @@ Certbot adheres to [Semantic Versioning](https://semver.org/).
 
 ### Added
 
-*
+* Fedora 29+ is now supported by certbot-auto. Since Python 2.x is on a deprecation
+  path in Fedora, certbot-auto will install and use Python 3.x on Fedora 29+.
 
 ### Changed
 

letsencrypt-auto-source/letsencrypt-auto

@@ -488,11 +488,18 @@ BOOTSTRAP_RPM_PYTHON3_VERSION=1
 BootstrapRpmPython3() {
   # Tested with:
   #   - CentOS 6
+  #   - Fedora 29
 
   InitializeRPMCommonBase
 
+  # Fedora 29 must use python3-virtualenv
+  if $TOOL list python3-virtualenv >/dev/null 2>&1; then
+    python_pkgs="python3
+      python3-virtualenv
+      python3-devel
+    "
   # EPEL uses python34
-  if $TOOL list python34 >/dev/null 2>&1; then
+  elif $TOOL list python34 >/dev/null 2>&1; then
     python_pkgs="python34
       python34-devel
       python34-tools
@@ -741,7 +748,10 @@ elif [ -f /etc/redhat-release ]; then
   prev_le_python="$LE_PYTHON"
   unset LE_PYTHON
   DeterminePythonVersion "NOCRASH"
-  if [ "$PYVER" -eq 26 ]; then
+  # Starting to Fedora 29, python2 is on a deprecation path. Let's move to python3 then.
+  RPM_DIST_NAME=`(. /etc/os-release && echo $ID) || echo "unknown"`
+  RPM_DIST_VERSION=`(. /etc/os-release && echo $VERSION_ID) || echo "0"`
+  if [ "$RPM_DIST_NAME" = "fedora" -a "$RPM_DIST_VERSION" -ge 29 -o "$PYVER" -eq 26 ]; then
     Bootstrap() {
       BootstrapMessage "RedHat-based OSes that will use Python3"
       BootstrapRpmPython3

letsencrypt-auto-source/letsencrypt-auto.template

@@ -323,7 +323,10 @@ elif [ -f /etc/redhat-release ]; then
   prev_le_python="$LE_PYTHON"
   unset LE_PYTHON
   DeterminePythonVersion "NOCRASH"
-  if [ "$PYVER" -eq 26 ]; then
+  # Starting to Fedora 29, python2 is on a deprecation path. Let's move to python3 then.
+  RPM_DIST_NAME=`(. /etc/os-release && echo $ID) || echo "unknown"`
+  RPM_DIST_VERSION=`(. /etc/os-release && echo $VERSION_ID) || echo "0"`
+  if [ "$RPM_DIST_NAME" = "fedora" -a "$RPM_DIST_VERSION" -ge 29 -o "$PYVER" -eq 26 ]; then
     Bootstrap() {
       BootstrapMessage "RedHat-based OSes that will use Python3"
       BootstrapRpmPython3

letsencrypt-auto-source/pieces/bootstrappers/rpm_python3.sh

@@ -5,11 +5,18 @@ BOOTSTRAP_RPM_PYTHON3_VERSION=1
 BootstrapRpmPython3() {
   # Tested with:
   #   - CentOS 6
+  #   - Fedora 29
 
   InitializeRPMCommonBase
 
+  # Fedora 29 must use python3-virtualenv
+  if $TOOL list python3-virtualenv >/dev/null 2>&1; then
+    python_pkgs="python3
+      python3-virtualenv
+      python3-devel
+    "
   # EPEL uses python34
-  if $TOOL list python34 >/dev/null 2>&1; then
+  elif $TOOL list python34 >/dev/null 2>&1; then
     python_pkgs="python34
       python34-devel
       python34-tools