build: solve m2e manifest problems

The m2e plugin for Eclipse IDE that many developers use is incompatible
with the cutting edge manifest-related maven plugins.

This patch downgrades the version of the maven-war-plugin (to 2.1.1) and
maven-ear-plugin (to 2.6), so that Eclipse can import the project with
not problems.

Change-Id: Ib678e50b9403ae16415f5e10fb8f1e9a58d77661
Signed-off-by: Allon Mureinik <amureini@redhat.com>