<!--- 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 -->

branches = get_branches(git_path, module, dest)
    for branch in branches:
        if branch.startswith('* ') and ('no branch' in branch or 'detached from' in branch or 'detached at' in branch):
            return True
    return False
def get_repo_path(dest, bare):
    if bare:
        repo_path = dest
    else:
        repo_path = os.path.join(dest, '.git')
    
    
    if os.path.isfile(repo_path):
        with open(repo_path, 'r') as gitfile:
            data = gitfile.read()
        ref_prefix, gitdir = data.rstrip().split('gitdir: ', 1)
        if ref_prefix:
            raise ValueError('.git file has invalid git dir reference format')
        
        if os.path.isabs(gitdir):
            repo_path = gitdir
        else:
            
            repo_path = os.path.join(dest, gitdir)
        if not os.path.isdir(repo_path):
            raise ValueError('%s is not a directory' % repo_path)
    return repo_path
def get_head_branch(git_path, module, dest, remote, bare=False):