Revising unit tests to use asserts instead of try/catch/except

There were many cases in the unit tests where try/catch/except
blocks could be replaced with self.assertRaises(...) instead.

By replacing the try/catch/except blocks the unit tests are
more readable.  Also very slightly decreases the time to run
all the unit tests.

Also some of the try/catch/except blocks were unneeded as a
failure in a unit test will already trigger an ERROR status.

Change-Id: Ia7e647e32b29d09fc205cb28732083e20fb4f988