core: Consolidating DiskValidator's RO validations

In DiskValidator:
isReadOnlyPropertyCompatibleWithLunInterface() was consolidated into
isReadOnlyPropertyCompatibleWithInterface().
Amended all existing tests in validator and related commands, Added
missing tests.

Some related tests did not follow unit-tests conventions and are
now corrected. Validator class in now the only one to test validator
inner flow. Other tests (commands) rely on expected input and should generate
the expected result according to that input.
The above note only applies to isReadOnlyPropertyCompatibleWithInterface()
usages.

Change-Id: I292f729c981df6563ec65d684e1b2b5ae12283a0
Signed-off-by: Vered Volansky <vvolansk@redhat.com>