Delete keys before incrementing them (test_itertypes)

Change-Id: If9c3dd6e824c633e4622f9681c70806f8193060b
Skip tx tests on Py3 or without twisted

Change-Id: I4a8cbda04765de32d214e38296ce1c4bed02aae4
tests.base: Fixup whitespace between class definitions

Change-Id: Ie2a3ecdee1fcb7aa1b42d6500a82e1b026ea0dd3
Don't import nose.exc in tests

Py 2.7 has 'unittest.case.SkipTest'. Import that first and fallback to
nose.exc.SkipTest

Change-Id: Ie6d64a019b3dbcc953e1b0a04796f9b11bf25ba0