<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
The `ssh_opts` parameter relies on setting environment variables for git, such as GIT_SSH. Git did not recognize this environment variable until version 2.3.0 (see https://git-scm.com/docs/git/2.3.0), and many contemporary OSes (RHEL 7, CentOS7) include older versions of Git (1.8.3.1).

It would be useful to provide a warning in this case, similar to the warning for the `depth` parameter. E.g. "Your git version is too old to support the ssh_opts argument."

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
git.py
source control, git module

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
It would save users time when trying to troubleshoot failed git connections via SSH.

<!--- Paste example playbooks or commands between quotes below -->
```yaml
- name: clone a git repo
  git:
    repo: git@github.com:cherdt/hello_ansible.git
    dest: /opt/hello_ansible
    version: master
    ssh_opts: "{{-o IdentityFile=github_id_rsa}}"
```

<!--- HINT: You can also paste gist.github.com links for larger files -->

''' samples the version of the git repo '''
    cmd = "%s rev-parse %s" % (git_path, ref)
    rc, stdout, stderr = module.run_command(cmd, cwd=dest)
    sha = to_native(stdout).rstrip('\n')
    return sha
def ssh_supports_acceptnewhostkey(module):
    try:
        ssh_path = get_bin_path('ssh')
    except ValueError as err:
        module.fail_json(
            msg='Remote host is missing ssh command, so you cannot '
            'use acceptnewhostkey option.', details=to_text(err))
    supports_acceptnewhostkey = True
    cmd = [ssh_path, '-o', 'StrictHostKeyChecking=accept-new', '-V']
    rc, stdout, stderr = module.run_command(cmd)
    if rc != 0:
        supports_acceptnewhostkey = False
    return supports_acceptnewhostkey
def get_submodule_versions(git_path, module, dest, version='HEAD'):