Commit 1c3231aa changed the invocation of _GetNodeRole() to pass the
master node by UUID and not by name, but didn't change the
implementation to compare the nodes by name. As a result, the master
node (which is also a master candidate) would always fall through to the
second option and be marked as 'C' instead as 'M'.

We fix this by modifying the implementation of _GetNodeRole() to perform
the comparison by UUID and also change the respective tests to test the
new API.

Signed-off-by: Apollon Oikonomopoulos <apoikos@gmail.com>
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>