<!--- 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 = "%s reset --hard %s/%s --" % (git_path, remote, branch)
    else:
        
        if is_remote_branch(git_path, module, dest, remote, version):
            if depth and not is_local_branch(git_path, module, dest, version):
                
                
                
                set_remote_branch(git_path, module, dest, remote, version, depth)
            if not is_local_branch(git_path, module, dest, version):
                cmd = "%s checkout --track -b %s %s/%s" % (git_path, version, remote, version)
            else:
                (rc, out, err) = module.run_command("%s checkout --force %s" % (git_path, version), cwd=dest)
                if rc != 0:
                    module.fail_json(msg="Failed to checkout branch %s" % version, stdout=out, stderr=err, rc=rc)
                cmd = "%s reset --hard %s/%s" % (git_path, remote, version)
        else:
            cmd = "%s checkout --force %s" % (git_path, version)
    (rc, out1, err1) = module.run_command(cmd, cwd=dest)
    if rc != 0:
        if version != 'HEAD':
            module.fail_json(msg="Failed to checkout %s" % (version),
                             stdout=out1, stderr=err1, rc=rc, cmd=cmd)
        else:
            module.fail_json(msg="Failed to checkout branch %s" % (branch),
                             stdout=out1, stderr=err1, rc=rc, cmd=cmd)
    if verify_commit:
        verify_commit_sign(git_path, module, dest, version, gpg_whitelist)
    return (rc, out1, err1)
def verify_commit_sign(git_path, module, dest, version, gpg_whitelist):