Make test_drivers.py use driver name from conf

test_list_drivers and test_show_driver in test_drivers.py use hard_coded
driver name.
This patch make these tests use driver name which is written in config file.

Closes-Bug: #1317717

Change-Id: Idad4c496a42c9253548fdf9020ffb8013fef951f
Merge "Make test_drivers.py use driver name from conf"