<!--- 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 not force:
                module.fail_json(msg="Local modifications exist in the destination: " + dest + " (force=no).", **result)
            
            if not module.check_mode:
                reset(git_path, module, dest)
                result.update(changed=True, msg='Local modifications exist in the destination: ' + dest)
        
        if module.check_mode:
            remote_url = get_remote_url(git_path, module, dest, remote)
            remote_url_changed = remote_url and remote_url != repo and unfrackgitpath(remote_url) != unfrackgitpath(repo)
        else:
            remote_url_changed = set_remote_url(git_path, module, repo, dest, remote)
        result.update(remote_url_changed=remote_url_changed)
        if module.check_mode:
            remote_head = get_remote_head(git_path, module, dest, version, remote, bare)
            result.update(changed=(result['before'] != remote_head or remote_url_changed), after=remote_head)
            
            if module._diff:
                diff = get_diff(module, git_path, dest, repo, remote, depth, bare, result['before'], result['after'])
                if diff:
                    result['diff'] = diff
            module.exit_json(**result)
        else:
            fetch(git_path, module, repo, dest, version, remote, depth, bare, refspec, git_version_used, force=force)
        result['after'] = get_version(module, git_path, dest)
    
    
    if not bare:
        switch_version(git_path, module, dest, remote, version, verify_commit, depth, gpg_whitelist)