Add command for Docker-style version information

This adds a command 'version' to show software versions information
like Docker does. In addition it includes:
- version of the docker-py-package
- Python-implementation and -version

Signed-off-by: Frank Sachsenheim <funkyfuture@riseup.net>

compose/cli/utils.py

@@ -1,10 +1,13 @@
 from __future__ import unicode_literals
 from __future__ import absolute_import
 from __future__ import division
+
+from .. import __version__
 import datetime
+from docker import version as docker_py_version
 import os
-import subprocess
 import platform
+import subprocess
 
 
 def yesno(prompt, default=None):
@@ -120,3 +123,15 @@ def is_mac():
 
 def is_ubuntu():
     return platform.system() == 'Linux' and platform.linux_distribution()[0] == 'Ubuntu'
+
+
+def get_version_info(scope):
+    versioninfo = 'docker-compose version: %s' % __version__
+    if scope == 'compose':
+        return versioninfo
+    elif scope == 'full':
+        return versioninfo + '\n' \
+            + "docker-py version: %s\n" % docker_py_version \
+            + "%s version: %s" % (platform.python_implementation(), platform.python_version())
+    else:
+        raise RuntimeError('passed unallowed value to `cli.utils.get_version_info`')