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: Ife6ee0d96bcfa448f746378a52d0102fd44a7a28
Merge "Utilize assertIsInstance"