core: Remove dead JPA implementation

Following a discussion on engine-devel
(http://lists.ovirt.org/pipermail/engine-devel/2012-December/003313.html,
http://lists.ovirt.org/pipermail/engine-devel/2013-January/003431.html)
and the partial removal of JPA-based DAOs as part of different
patches (e.g., change-id I1c1adda55bd27beef2907bf0ed8a0f8bc274e495),
this patch completely removes JPA implementation for the project.
Note this is code is unused in the system and is no longer maintained
anyway, so even it it were enabled, it would no longer work.

This patch removes the following:
* JPA annotations from business entities
* Hibernate-specific mapping annotations from said business entities
  (validation annotations were left in tact, just to be on the safe
  side).
* Fields in said business entities that were not used, but only
  referenced by said annotations.
* JPA context configuration for said classes.
* Classes only used by said annotations - GuidType and GuidGenerator.
* Methods in ReflectionUtils that were only relevant to the removed
  @Table and @column annotations.
* Testing code in GeneralDbDAOTest that tested said annotations.
* JPA based DAOs - *DaoHibernateImpl and *WrapperDaoImpl
* Testing code in the DAO test framework only used to set up JPA
  sessions.
* Resources and documentation for those tests.
* References to unused JPA and hibernate jars in the relevant pom.xml
  files. The removal of JPA from the common project forced the addition
  of JTA to the bll and vdsbroker projects, since they were no longer
  implicitly dependant on it (via common->jpa->jta). However, this
  addition makes bll and vdsbroker's pom.xmls clearer, as they do
  explicitly use JTA classes.

Change-Id: I6ea15c96900f0c23d2fd5d5174bd8e90a44aa53a
Signed-off-by: Allon Mureinik <amureini@redhat.com>