<!--- 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 -->

import os
import re
import shlex
import stat
import sys
import shutil
import tempfile
from ansible.module_utils.compat.version import LooseVersion
from ansible.module_utils._text import to_native, to_text
from ansible.module_utils.basic import AnsibleModule
from ansible.module_utils.common.locale import get_best_parsable_locale
from ansible.module_utils.common.process import get_bin_path
from ansible.module_utils.six import b, string_types
def relocate_repo(module, result, repo_dir, old_repo_dir, worktree_dir):
    if os.path.exists(repo_dir):
        module.fail_json(msg='Separate-git-dir path %s already exists.' % repo_dir)
    if worktree_dir:
        dot_git_file_path = os.path.join(worktree_dir, '.git')
        try:
            shutil.move(old_repo_dir, repo_dir)
            with open(dot_git_file_path, 'w') as dot_git_file:
                dot_git_file.write('gitdir: %s' % repo_dir)
            result['git_dir_before'] = old_repo_dir
            result['git_dir_now'] = repo_dir
        except (IOError, OSError) as err:
            
            if os.path.exists(repo_dir):
                shutil.move(repo_dir, old_repo_dir)
            module.fail_json(msg=u'Unable to move git dir. %s' % to_text(err))
def head_splitter(headfile, remote, module=None, fail_on_error=False):