One problem I ran into a lot with that 'virsh net create' test is unexpected things do happen unexpectedly :)  There's a lot of things happening between setup and recovery, if one thing breaks, recovery may not happen.  I would like to see a <code>try...finally</code> construct around the "test case", to guarantee recovery happens.  

Otherwise the test system could be left with a messed up network that may impact all following tests.  One strategy that can be helpful (to limit amount of indentation) is to make a separate function for the test code, then just call that inside <code>try...finally</code>.  Though just nesting everything inside a giant <code>try</code> is probably okay also.