Allow refspec in role fetcher
Allow refspec in role fetcher

This allows specification in the ansible-role-requirements to pull
a role directly from a gerrit change.

Example:
- name: os_neutron
  scm: git
  src: https://git.openstack.org/openstack/openstack-ansible-os_neutron
  version: FETCH_HEAD
  refspec: '+refs/changes/24/391524/*:refs/remotes/origin/changes/24/391524/*'

This will pull the latest revision of change 391524.

Change-Id: I96666f349d6f0317d51735146e94c3bd12c7ef6f

cfarquhar/openstack-ansible,BjoernT/os-ansible-deployment,cloudnull/os-ansible-deployment,openstack/openstack-ansible,BjoernT/os-ansible-deployment,stackforge/os-ansible-deployment,robb-romans/openstack-ansible,BjoernT/os-ansible-deployment,stackforge/os-ansible-deployment,BjoernT/openstack-ansible,bunchc/openstack-ansible,openstack/openstack-ansible,Logan2211/openstack-ansible,cfarquhar/openstack-ansible,Logan2211/openstack-ansible,os-cloud/os-ansible-deployment,bunchc/openstack-ansible,BjoernT/openstack-ansible,weezer/openstack-ansible,weezer/openstack-ansible,robb-romans/openstack-ansible,cloudnull/os-ansible-deployment,os-cloud/os-ansible-deployment,yanyao/openstack-ansible,yanyao/openstack-ansible