Install OVS from source when it was configured like that

Function _neutron_ovs_base_install_agent_packages always tried to
install openvswitch from packages and start it using systemd units.
That was failing when ovs was expected to be installed from source.
This patch fixes that.

Change-Id: Iae8625dd800d30061ea3dbed9eb0dfbe16f21572
diff --git a/lib/neutron_plugins/ovs_source b/lib/neutron_plugins/ovs_source
index 08951d1..9c87dce 100644
--- a/lib/neutron_plugins/ovs_source
+++ b/lib/neutron_plugins/ovs_source
@@ -14,6 +14,7 @@
 
 # Defaults
 # --------
+Q_BUILD_OVS_FROM_GIT=$(trueorfalse False Q_BUILD_OVS_FROM_GIT)
 
 # Set variables for building OVS from source
 OVS_REPO=${OVS_REPO:-https://github.com/openvswitch/ovs.git}