relocatable roots doesn't handle testr args/opts

Previous fix (4c891b9243985bb95d8beff8affa9db470a1c94a)
changed how the args are parsed but didn't update the logic
for handling testr args/opts. As a result args/opts for testr
where not be properly passed.

This fixes corrects that oversite and now properly parses those
args as well.

Change-Id: I418b0478b2a180e497d041fcab25158c52f44bac
Fixes: #1116942
Merge "relocatable roots doesn't handle testr args/opts"