<!--- 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 version in get_annotated_tags(git_path, module, dest):
        git_sub = "verify-tag"
    else:
        git_sub = "verify-commit"
    cmd = "%s %s %s" % (git_path, git_sub, version)
    if gpg_whitelist:
        cmd += " --raw"
    (rc, out, err) = module.run_command(cmd, cwd=dest)
    if rc != 0:
        module.fail_json(msg='Failed to verify GPG signature of commit/tag "%s"' % version, stdout=out, stderr=err, rc=rc)
    if gpg_whitelist:
        fingerprint = get_gpg_fingerprint(err)
        if fingerprint not in gpg_whitelist:
            module.fail_json(msg='The gpg_whitelist does not include the public key "%s" for this commit' % fingerprint, stdout=out, stderr=err, rc=rc)
    return (rc, out, err)
def get_gpg_fingerprint(output):
    """Return a fingerprint of the primary key.
    Ref:
    https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob;f=doc/DETAILS;hb=HEAD#l482
    """
    for line in output.splitlines():
        data = line.split()
        if data[1] != 'VALIDSIG':
            continue
        
        data_id = 11 if len(data) == 11 else 2
        return data[data_id]
def git_version(git_path, module):