Modify unit test to cover more cases

[RezaYazdaniAminabadi]

This PR adds two set of modification to the unit tests for better test coverage on optimizer functionality:

1. Increase the parameters groups to catch errors better at optimizer step function.
2. Reduce the loss scale by using "initial_scale_power" to reduce the likelihood of overflowing in the backward and the optimizer step will be called into eventually.

cc: @tjruwase, @jeffra

[rocm-mici]

Can one of the admins verify this patch?