Utilize assertIsInstance

Using assertTrue and the 'isinstance' function to test
if an object is in an instance of some class is too python2.4.
Our unit testing framework supports assertIsInstance which was created
for these types of tests. Let's use assertIsInstance for these tests.

Change-Id: I2c931a52ae20f072f53210bf3dedb47127b413c0
Merge "Utilize assertIsInstance"