Native charm support

This commit adds an API Proxy env variable to __lcm__.env, in order to
enable native charm support in OSM.

The default behavior is to automatically detect the IP of the primary
interface. This can be overridden with the -A flag.

Change-Id: I172ce4f7bb76f67ae9fb8918cdd5a10c93fa3b8a
Signed-off-by: Adam Israel <adam.israel@canonical.com>