core, restapi: Remove double ReapedMaps

There are two almost identical (except for whitespaces and the
occasional formatting difference) classes called ReadpedMap in oVirt
Engine:
1. org.ovirt.engine.api.common.util.ReapedMap
2. org.ovirt.engine.core.utils.ReapedMap

This patch removes the api class, and leaves only the core one.
It includes:
1. Removal of the redundant class and deferring all usages to the
   correct class.
2. Moving the test from the rest package to the core package.
3. Translating the test from EasyMock to Mockito, as used in the rest of
   the core package tests.

Change-Id: I924355a495945a063b8e15f233188fc236df2432
Signed-off-by: Allon Mureinik <amureini@redhat.com>