<!--- 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 -->

cmd = [git_path, 'clone']
    if bare:
        cmd.append('--bare')
    else:
        cmd.extend(['--origin', remote])
    is_branch_or_tag = is_remote_branch(git_path, module, dest, repo, version) or is_remote_tag(git_path, module, dest, repo, version)
    if depth:
        if version == 'HEAD' or refspec:
            cmd.extend(['--depth', str(depth)])
        elif is_branch_or_tag:
            cmd.extend(['--depth', str(depth)])
            cmd.extend(['--branch', version])
        else:
            
            module.warn("Ignoring depth argument. "
                        "Shallow clones are only available for "
                        "HEAD, branches, tags or in combination with refspec.")
    if reference:
        cmd.extend(['--reference', str(reference)])
    if single_branch:
        if git_version_used is None:
            module.fail_json(msg='Cannot find git executable at %s' % git_path)
        if git_version_used < LooseVersion('1.7.10'):
            module.warn("git version '%s' is too old to use 'single-branch'. Ignoring." % git_version_used)
        else:
            cmd.append("--single-branch")
            if is_branch_or_tag:
                cmd.extend(['--branch', version])
    needs_separate_git_dir_fallback = False
    if separate_git_dir: