Allow packages to be updated on their own

In some cases, it is required to let packages update themselves:
- Some Windows updates increase the version number of installed packages
  while this version cannot be deployed standalone through a regular
  win_repo package
- Allow users to apply timely critical updates on their own so they
  don't have to wait for the admins to provide the newest version (e.g
  auto updates of software such as Mozilla Firefox which allows to
  install updates through regular users without administrative
  permissions)

Fixes #11602
Fixes 12702: now a traceback exc is written when returner fails
auto accept keys in minions_autosign

Accept keyids if a file with the same name is found in minions_autosign.
Also option to check the datestamp of the file and only accept if within timeout.
Merge pull request #12723 from gtmanfred/develop

Fixes #12719
Improve jinja error reporting

Salt execution functions routinely raise SaltInvocationError and
CommandExecutionError exceptions. This commit catches them in the jinja
renderer and provides a nicely-formatted error message, preventing the
traceback from being in the render error that is printed to the CLI.
Raise exceptions when trying to read nonexistant files

Prevents a traceback when an invalid timezone is passed
Catch exceptions raised when comparing timezone
Fix syntax error in nova.py

get('id', None} should be get('id', None)
Fix lint failure
Update nova.py

I somehow reversed two letters in time.
Merge pull request #12726 from grue/patch-1

Fix syntax error in nova.py
Update documentation in salt/states/postgres_extension.py
Clarify comments in postgres_extension.py
Add a grain for the python executable in use
Merge pull request #12733 from s0undt3ch/features/python-executable-grain

Add a grain for the python executable in use
Added missing whitespaces after comma to prevent lint-errors.
service.available should also use chkconfig, to support xinetd services
redis external pillar, more redis exec
Merge pull request #12724 from terminalmage/issue12696

Jinja renderer, timezone module/state fixes
Merge pull request #12711 from eliasp/states_pkg-allow_updates

Allow packages to be updated on their own