<!--- 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 -->

if refspecs:
            
            
            
            
            fetch_cmd.extend(['--depth', str(depth)])
    if not depth or not refspecs:
        
        
        if bare:
            refspecs = ['+refs/heads/*:refs/heads/*', '+refs/tags/*:refs/tags/*']
        else:
            
            if git_version_used >= LooseVersion('1.9'):
                fetch_cmd.append('--tags')
            else:
                
                commands.append((fetch_str, fetch_cmd + [remote]))
                refspecs = ['+refs/tags/*:refs/tags/*']
        if refspec:
            refspecs.append(refspec)
    if force:
        fetch_cmd.append('--force')
    fetch_cmd.extend([remote])
    commands.append((fetch_str, fetch_cmd + refspecs))
    for (label, command) in commands:
        (rc, out, err) = module.run_command(command, cwd=dest)
        if rc != 0:
            module.fail_json(msg="Failed to %s: %s %s" % (label, out, err), cmd=command)
def submodules_fetch(git_path, module, remote, track_submodules, dest):