core: Serializable LastTimeUsedAsMasterComp

Made LastTimeUsedAsMasterComp Serializeable, as per the FindBugs
warning.

Change-Id: I5a30def7a132a7d53a57e57acbf9b61132a9bff6
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: JDK7 impl. for LastTimeUsedAsMasterComp

Used the JDK7 standard implementation, now that BLL supports JDK7.

Change-Id: I8bc24521c02c5198a510086a017ccef0c17a2e2c
Signed-off-by: Allon Mureinik <amureini@redhat.com>