[BUG] Git module and states are broken in multiple ways

Description

1. git state fails if rev is SHA1
2. logging is uninformative unless you set GIT_SSH_COMMAND="ssh -v " environ
3. (pretty sure, but not completely) GIT_IDENTITY env of git is nowhere to be found, but is used here. I'm pretty sure it's useless and must be rewtitten to GIT_SSH_COMMAND="ssh -i "

First of all - without GIT_SSH_COMMAND="ssh -v" (see states below) logging is useless. You would always receive this:

12:43:54 [INFO    ] File /root/.ssh/repo-sync-key is in the correct state [salt.state]
12:43:54 [INFO    ] Completed state [/root/.ssh/repo-sync-key] at time 12:43:54.973777 (duration_in_ms=32.855) [salt.state]
12:43:54 [INFO    ] Running state [git+ssh://git@<local mirror URL>/gentoo-mirror] at time 12:43:54.974039 [salt.state]
12:43:54 [INFO    ] Executing state git.latest for [git+ssh://git@<local mirror URL>/gentoo-mirror] [salt.state]
12:43:54 [INFO    ] Executing command ['git', 'config', '--global', '--get-regexp', 'filter\\.lfs\\.'] in directory '/root' [salt.loaded.int.module.cmdmod]
12:43:54 [DEBUG   ] retcode: 1 [salt.loaded.int.module.cmdmod]
12:43:54 [INFO    ] Checking remote revision for git+ssh://git@<local mirror URL>/gentoo-mirror [salt.loaded.int.states.git]
12:43:54 [INFO    ] Attempting git authentication using identity file /root/.ssh/repo-sync-key [salt.loaded.int.module.git]
12:43:54 [INFO    ] Executing command ['git', 'ls-remote', 'git+ssh://git@<local mirror URL>/gentoo-mirror'] in directory '/root' [salt.loaded.int.module.cmdmod]
12:43:55 [ERROR   ] Command '['git', 'ls-remote', 'git+ssh://git@<local mirror URL>/gentoo-mirror']' failed with return code: 128 [salt.loaded.int.module.cmdmod]
12:43:55 [ERROR   ] stderr: git@<local mirror URL>: Permission denied (keyboard-interactive).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists. [salt.loaded.int.module.cmdmod]

I know this because at first I missed part of the docs that says you must not set depth parameter when setting rev to SHA1 instead of branch/tag. But kept getting the same Permission denied error and was looking in wrong direction.

So after a bit of digging into the modules/git.py and states/git.py I found out that module is using unfamiliar GIT_IDENTITY to set private key path. I desided to explicitly set GIT_SSH_COMMAND="ssh -vvv -i /root/.ssh/repo-sync-key" via another state and voila! The error message became informative and I saw this error.

And the last thing about GIT_IDENTITY - it turned out that I had .ssh/config with IdentityFile /root/.ssh/repo-sync-key set there all the time (so -i /root/.ssh/repo-sync-key earlier was excessive and it was -vvv part that mattered - I guess I was lucky to catch the problem at all). I removed IdentityFile from ssh config, -i part from GIT_SSH_COMMAND, but kept identity definition in the state and received the same Permission denied error I was getting earlier. From here I deduced that GIT_IDENTITY env is pretty much useless and identity feature in git.latest state is broken.

To clarify - the private key and .ssh have all the nesessary permissions and I'm able to work with the repo directly with git from OS.

And last, but not least - when you set rev to SHA1 you get this:

----------
          ID: gentoo-repo
    Function: git.latest
        Name: git+ssh://git@<local mirror URL>/gentoo-mirror
      Result: False
     Comment: Fetch did not successfully retrieve rev '7b901fbb06' from git+ssh://git@<local mirror URL>/gentoo-mirror: Command 'git rev-parse 7b901fbb06^{commit}' failed: fatal: ambiguous argument '7b901fbb06^{commit}': unknown revision or path not in the working tree.
              Use '--' to separate paths from revisions, like this:
              'git <command> [<revision>...] -- [<file>...]'
     Changes:

The exception is catched here. It's obvious for me that we should check if ^{commit} should be appended to the revision before invoking git rev-parse.

Setup
To reproduce you would need a git repository that works over git+ssh with publickey auth.
This is the state file to reproduce issue 1. git state fails if rev is SHA1

>>> gentoo/repos/gentoo.sls
include:
  - .keys # sync .ssh/config and .ssh/repo-sync-key

setenv:
  environ.setenv:
    - name: GIT_SSH_COMMAND
    - value: "ssh -v"

gentoo-repo:
  git.latest:
    - name: git+ssh://git@<local mirror URL>/gentoo-mirror
    - target: /usr/portage
    - rev: 7b901fbb06              # <---------- the only relevant thing here
    - identity: /root/.ssh/repo-sync-key
    - force_clone: True
    - force_checkout: True
    - reload_modules: True
    - require:
      - file: /root/.ssh/repo-sync-key
      - environ: setenv

To reprodure 2. logging is uninformative unless you set GIT_SSH_COMMAND="ssh -v " environ remove setenv state.

To reproduce 3. GIT_IDENTITY env of git is nowhere to be found remove .ssh/config or comment out IdentityFile part.

Steps to Reproduce the behavior
Run salt-call state.sls gentoo.repos.gentoo in each of 3 cases.

Expected behavior

1. Provided SHA1 commit is checked out when rev: <SHA1> is present in the state definition.
2. Logging is informative.
3. Authentication is successful when path to correct identity file is provided in the state definition.

Versions Report

On master:

</details>

Start by reproducing the three cases with salt-call state.sls gentoo.repos.gentoo using the provided state file and version details. Read the referenced logic in salt/modules/git.py and salt/states/git.py, especially the linked identity handling and rev-parse paths. Done means SHA1 revisions check out, SSH diagnostics are informative, and the state’s identity path authenticates successfully.