integrationtest: solve a build warning

integrationtest: solve a build warning

When building mappingservice/integrationtest, I get the following
warning:

[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.opendaylight.lispflowmapping:mappingservice.integrationtest:jar:0.5.1-SNAPSHOT
[WARNING] 'parent.relativePath' points at org.opendaylight.lispflowmapping:mappingservice-parent instead of org.opendaylight.controller:commons.integrationtest, please verify your project structure @ line 6, column 10
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]

This commit solves the warning, by explicitly specifying an empty
parent.relativePath.

Change-Id: I81e2334aeba6a9f135f49d1ed8a3cc444b9079ee
Signed-off-by: Lorand Jakab <lojakab@cisco.com>