Add support for marking test cases as requiring a certain topology. The
default topology is a two link topology and the other supported
topologies are one link and no link topologies.

The TestProtocol of test suites and cases is extended with the topology
type each test suite or case requires. Each test case starts out as
requiring a two link topology and can be marked as requiring as
topology directly (by decorating the test case) or through its test
suite. If a test suite is decorated as requiring a certain topology, all
its test cases are marked as such. If both test suite and a test case
are decorated as requiring a topology, the test case cannot require a
more complex topology than the whole suite (but it can require a less
complex one). If a test suite is not decorated, this has no effect on
required test case topology.

Since the default topology is defined as a reference to one of the
actual topologies, the NoAliasEnum from the aenum package is utilized,
which removes the aliasing of Enums so that TopologyType.two_links and
TopologyType.default are distinct. This is needed to distinguish between
a user passed value and the default value being used (which is used when
a test suite is or isn't decorated).

Signed-off-by: Juraj Linkeš <juraj.linkes@pantheon.tech>