Create nodepool_git_update varible

First attempt to support offline install, as it is possible for the
git repo to already be installed onto disk. This is the case now in
zuulv3, we no longer need to fetch git from a repo location.

Change-Id: Ic93ccb65014619131e335dd0d5bb2ae3c21ae98b
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

defaults/main.yaml

@@ -59,6 +59,7 @@ nodepool_git_dest: /opt/ansible-role-nodepool/git/openstack-infra/nodepool
 nodepool_git_uri: https://git.openstack.org/openstack-infra/nodepool
 nodepool_git_version: feature/zuulv3
 # nodepool_git_refspec:
+# nodepool_git_update:
 
 nodepool_install_method: git
 

tasks/install/git.yaml

@@ -18,6 +18,7 @@
     dest: "{{ nodepool_git_dest }}"
     refspec: "{{ nodepool_git_refspec|default(omit) }}"
     repo: "{{ nodepool_git_uri }}"
+    update: "{{ nodepool_git_update|default(omit) }}"
     version: "{{ nodepool_git_version|default(omit) }}"
 
 - name: Set nodepool_pip_name to local git repo.