Modify system shutdown command.

New flag to shutdown at a given time. Refs #7833.
yaml.dumps() doesn't exist. Use dump().
Document how to run salt-ssh as unprivileged user.
git: new `git.ls_remote` with similar interface than other Git functions

Inspired from salt.states.git.__ls_remote__, which it aims to replace.
git: use the new git.ls_remote function

The interface of this function is similar to the other Salt Git's functions
and it uses the 'identity' settings which is set in the state.

Fixes #8094
Merge pull request #8246 from multani/fix/8094-ls-remote-use-ssh-key

State git.latest's "ls-remote" step uses the specified SSH key
updated salt spec file for 0.17.1
disabled unit testing until next version broken with salt-testing 0.5.2
Fix --output-file CLI argument

This commit fixes it so that the file in not overwritten each time a
minion returns information. Fixes #8205.
Stop the `__virtualname__` deprecation warning. Fixes #8221.
Remove existing output file if present

This saves the use of a filehandle by simply removing the file instead
of truncating it. when salt.output.display_output comes along to append
to the file, it will be created if it does not already exist.
Merge pull request #8258 from terminalmage/issue8205

Fix --output-file CLI argument
Add note to pkgrepo states when run with test=True
Merge pull request #8256 from cachedout/sys-shutdown

Modify system shutdown command.
Merge pull request #8255 from aboe76/develop

updated salt spec file for 0.17.1
Updated Dash URL for https
Added an explanation of grains.filter_by and the merge kwarg to formula

Fixes #8239
Merge pull request #8265 from s0undt3ch/develop

Stop the `__virtualname__` deprecation warning. Fixes #8221.
Correctly detect a git checkout. Refs #8090. Fixes #8266.

The problem is that when we `exec()` the version code from `setup.py`, the `__file__` paths changed and we were "missing" the `.git` directory.
Merge pull request #8268 from s0undt3ch/develop

Correctly detect a git checkout. Refs #8090. Fixes #8266.
Remove stray print