<!--- 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 umask is not None:
        if not isinstance(umask, string_types):
            module.fail_json(msg="umask must be defined as a quoted octal integer")
        try:
            umask = int(umask, 8)
        except Exception:
            module.fail_json(msg="umask must be an octal integer",
                             details=to_text(sys.exc_info()[1]))
        os.umask(umask)
    
    
    if os.path.expanduser(repo).startswith('/'):
        repo = 'file://' + os.path.expanduser(repo)
    
    
    locale = get_best_parsable_locale(module)
    module.run_command_environ_update = dict(LANG=locale, LC_ALL=locale, LC_MESSAGES=locale, LC_CTYPE=locale)
    if separate_git_dir:
        separate_git_dir = os.path.realpath(separate_git_dir)
    gitconfig = None
    if not dest and allow_clone:
        module.fail_json(msg="the destination directory must be specified unless clone=no")
    elif dest:
        dest = os.path.abspath(dest)
        try:
            repo_path = get_repo_path(dest, bare)
            if separate_git_dir and os.path.exists(repo_path) and separate_git_dir != repo_path:
                result['changed'] = True
                if not module.check_mode: