[simulation mode] implement mock context manager for Murano

Context manager is responsible for providing a valid context with corresponding attributes and functions for the current object. Modified context manager will be used for mock implementation. It will be inherited from the original one and will be called ``MockContextManager``. It will store instructions ...

Mocking machinery for muranopl testing framework for Murano

user should be able to use mock for Heat and murano-agent at least. To realize this, mocks are needed: they should be configurable, user should be able to set a return value.