Refactor service readiness notification

Build upon cceda95a35f18f5f7b52daaf0662a4cd3768b3ac apply Oslo systemd
module. It was imported in aef33d2d716c064f1f571c334fd36b1ea5928d5c. It
also drops heat.common.systemd and deprecates onready configuration
parameter.

Oslo commit 53e1214c092f09e3851b1a1b55289a93a72b09ec

Change-Id: I80f325c9be9c171c2dc8d5526570bf64f0f87c78
Improve mocking in HeatTestCase

As the mock lib is going to be used more actively, there is a need
to improve our boilerplate code in respect to mock.

Changes in this patch include:
* `patchobject` now accepts kwargs and passes them to `mock.patch.object`;
* added `patch` method that uses mock.patch (similar to `patchobject`)
  - NOTE: this shadows `testtools.TestCase.patch` method that uses
    simple monkey-patching in favor of mock-based patching,
    relevant comment added in the code;
* test code changed accordingly where needed.

Change-Id: I779cab63249d5eb1962e9ec388cd31f3df4a4189
Fix monkey-patching occurence in a test

A test of Resource class was using a direct monkey-patching of a
generic resource class without cleanup. This has not resulted in an error
so far, but surely might in the future.

This patch uses proper mock for patching instead.

Change-Id: I9134dfc625e12df1ebcacda8373f81737fd59c2c
Merge "Refactor service readiness notification"