* Change Mock API to match mockNetConn Expect* calls.
* Make logging.NewMock take and store *testing.T.
* Add a level-agnostic Expect().
* Make writerMap an externally accessible type.
* Adjust tests to take this shaving into account.
1) Adjust alignments for exp/got correctly.
2) Print expected string when nothing logged at level.
3) Check to ensure no unexpected logging occurred at other levels when nothing
logged at expected level.