<!--- 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 -->

relocate_repo(module, result, separate_git_dir, repo_path, dest)
                    repo_path = separate_git_dir
        except (IOError, ValueError) as err:
            
            """``.git`` file does not have a valid format for detached Git dir."""
            module.fail_json(
                msg='Current repo does not have a valid reference to a '
                'separate Git dir or it refers to the invalid path',
                details=to_text(err),
            )
        gitconfig = os.path.join(repo_path, 'config')
    
    
    
    ssh_wrapper = write_ssh_wrapper(module.tmpdir)
    set_git_ssh(ssh_wrapper, key_file, ssh_opts)
    module.add_cleanup_file(path=ssh_wrapper)
    git_version_used = git_version(git_path, module)
    if depth is not None and git_version_used < LooseVersion('1.9.1'):
        module.warn("git version is too old to fully support the depth argument. Falling back to full checkouts.")
        depth = None
    recursive = module.params['recursive']
    track_submodules = module.params['track_submodules']
    result.update(before=None)
    local_mods = False
    if (dest and not os.path.exists(gitconfig)) or (not dest and not allow_clone):