Bug 1896: L3 router interface not being installed

Fix code path where tenant instance is added to node after router interface
is created.

Patch 2: code review. Thanks Mr. T!  :)

Change-Id: I466f1c45cde8f3002b20cfb0f43b9e791a0031bf
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>
Merge "Bug 1896: L3 router interface not being installed"