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##### SUMMARY

The Git module encourages use of `StrictHostKeyChecking=no` with SSH, which makes the connection vulnerable to a MITM attack.

##### ISSUE TYPE

OpenSSH 7.5+ (2017-03-20) added a safer option which automatically accepts the key on first use but will not allow a MITM on subsequent connections: `StrictHostKeyChecking=accept-new` 

https://man.openbsd.org/ssh_config#StrictHostKeyChecking

It would be great if Ansible encouraged use of that mode by default in the documentation and to implement features such as the Git module's [`accept_hostkey`](https://github.com/ansible/ansible/blob/323d2adfcce9a53e906c2c4a40f6ac5fb32a0e68/lib/ansible/modules/git.py#L1103-L1108) feature.

##### ANSIBLE VERSION

```paste below
N/A
```

##### COMPONENT NAME
* `/modules/source_control/git.py`


'''
    Resets the index and working tree to HEAD.
    Discards any changes to tracked files in working
    tree since that commit.
    '''
    cmd = "%s reset --hard HEAD" % (git_path,)
    return module.run_command(cmd, check_rc=True, cwd=dest)
def get_diff(module, git_path, dest, repo, remote, depth, bare, before, after):
    ''' Return the difference between 2 versions '''
    if before is None:
        return {'prepared': '>> Newly checked out %s' % after}
    elif before != after:
        
        git_version_used = git_version(git_path, module)
        fetch(git_path, module, repo, dest, after, remote, depth, bare, '', git_version_used)
        cmd = '%s diff %s %s' % (git_path, before, after)
        (rc, out, err) = module.run_command(cmd, cwd=dest)
        if rc == 0 and out:
            return {'prepared': out}
        elif rc == 0:
            return {'prepared': '>> No visual differences between %s and %s' % (before, after)}
        elif err:
            return {'prepared': '>> Failed to get proper diff between %s and %s:\n>> %s' % (before, after, err)}
        else:
            return {'prepared': '>> Failed to get proper diff between %s and %s' % (before, after)}
    return {}
def get_remote_head(git_path, module, dest, version, remote, bare):