<!--- 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 -->

An example value could be "-o StrictHostKeyChecking=no"
              (although this particular option is better set by
              I(accept_hostkey)).
        type: str
        version_added: "1.5"
    key_file:
        description:
            - Specify an optional private key file path, on the target host, to use for the checkout.
        type: path
        version_added: "1.5"
    reference:
        description:
            - Reference repository (see "git clone --reference ...").
        version_added: "1.4"
    remote:
        description:
            - Name of the remote.
        type: str
        default: "origin"
    refspec:
        description:
            - Add an additional refspec to be fetched.
              If version is set to a I(SHA-1) not reachable from any branch
              or tag, this option may be necessary to specify the ref containing
              the I(SHA-1).
              Uses the same syntax as the C(git fetch) command.
              An example value could be "refs/meta/config".
        type: str
        version_added: "1.9"
    force: