Bug 577552 - Switch tests to mockito

Switch p2 tests to mockito from easymock.
Improve asserts to be slightly more readable and give better failure
message.

Change-Id: I3b975983a5c975dc03814a73bdbf0ce9ed652a1f
Signed-off-by: Alexander Kurtakov <akurtako@redhat.com>
Reviewed-on: https://git.eclipse.org/r/c/equinox/rt.equinox.p2/+/188640
Tested-by: Equinox Bot <equinox-bot@eclipse.org>
21 files changed