Fix sed regex for deleting old configs

Ic968f39b16934c9e55d9aa448cbd9de54f659d4d removed the "auto $bridge" line
from the bridge configuration so we need to update the sed to continue to
remove that section, which now starts with the "allow-ovs $bridge" line instead

Change-Id: I76df0d00f2f01e2945570b94abfb78dd73c7b240
Merge "Fix sed regex for deleting old configs"