Add test skip decorator when service not available

Adding services_required decorator that can be used for decorating test classes
as well as test methods. Decorator expects as arguments services that
should be available during test execution.

Skipping decorators are not available in the nose python library,
therefore custom skipping decorator has to be made.

Partially implements blueprint: selenium-integration-testing

Change-Id: I6de4ec75ef9dc56f1ed11057d8b30bb0a782c6e3
Merge "Add test skip decorator when service not available"