BUG-2626: activate enunciate only on jdk-1.7

The plugin is not supported with JDK8. Create two parent pom.xmls, one
of which defines the activation on JDK7 only and the second one
centralizes the AD-SAL definitions for it.

Change-Id: I791847d6e27dae0f51499b303cbea9163f5f184a
Signed-off-by: Robert Varga <rovarga@cisco.com>