ovs_base: Fix debug-agent config for Q_USE_PROVIDERNET_FOR_PUBLIC=True

Set up external_network_bridge correctly for the case
of Q_USE_PROVIDERNET_FOR_PUBLIC=True.

This is an oversight in commit 6a633fd024347aade777ecd6545fa3efde5a959c.

Closes-Bug: #1394826
Change-Id: I33f0fe15bafb7071d8a09899d636471f49031606
IPA Ramdisk should log to console in devstack

Setting these kernel command line parameters will have journald log
everything to the console, which means it'll end up in the appropriate
log in the ironic-bm-logs/ directory.

Change-Id: I0f4c79436c4856a5aa72f00f1ac8c2ed534b702e
Merge "IPA Ramdisk should log to console in devstack"
Merge "ovs_base: Fix debug-agent config for Q_USE_PROVIDERNET_FOR_PUBLIC=True"