Add project group to role
Add project group to role

This patch adds a var used by the repo_build process to determine
which host group to check for members of before building the pip
packages required by this role. This provides the ability to
optimise the repo build process to only building the packages
that are required for an environment.

Depends-On: Idda16b4f382eee57c7469af898859d6d81d4eb30
Change-Id: Iedb4c0c91daa291f881a9fc00c5b8c40bb312ce3

juledwar/openstack-ansible-os_ironic,juledwar/openstack-ansible-os_ironic