packaging: provide activation.jar

activation.jar is required by hibernate-validator, which causes maven to
bring it as a transient dependency, even though it is part of the JDK.

Explicitly adding it to the root pom.xml and marking it as provided (in
a similar fashion to javax.transaction) makes sure it is not brought
twice.

Change-Id: If6bbed19bee01bcd76b15e709f50810b88aaa973
Signed-off-by: Allon Mureinik <amureini@redhat.com>