<!--- 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 -->

'''Extract the head reference'''
    
    res = None
    if os.path.exists(headfile):
        rawdata = None
        try:
            f = open(headfile, 'r')
            rawdata = f.readline()
            f.close()
        except Exception:
            if fail_on_error and module:
                module.fail_json(msg="Unable to read %s" % headfile)
        if rawdata:
            try:
                rawdata = rawdata.replace('refs/remotes/%s' % remote, '', 1)
                refparts = rawdata.split(' ')
                newref = refparts[-1]
                nrefparts = newref.split('/', 2)
                res = nrefparts[-1].rstrip('\n')
            except Exception:
                if fail_on_error and module:
                    module.fail_json(msg="Unable to split head from '%s'" % rawdata)
    return res
def unfrackgitpath(path):