Add docstrings for <method>_FORBIDDEN usage
Add docstrings for <method>_FORBIDDEN usage

This patch expands the docstrings of the RAPI metaclass with
information on the new FORBIDDEN parameter definitions.

Signed-off-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

dimara/ganeti,yiannist/ganeti,apyrgio/ganeti,mbakke/ganeti,apyrgio/ganeti,andir/ganeti,ganeti/ganeti,grnet/snf-ganeti,leshchevds/ganeti,dimara/ganeti,onponomarev/ganeti,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,andir/ganeti,yiannist/ganeti,leshchevds/ganeti,grnet/snf-ganeti,leshchevds/ganeti,yiannist/ganeti,bitemyapp/ganeti,mbakke/ganeti,ganeti/ganeti,andir/ganeti,bitemyapp/ganeti,ganeti-github-testing/ganeti-test-1,mbakke/ganeti