Require testrepository and other tools at runtime

Normally we don't want testrepository and some of the other
related tools to be required at runtime, so they are listed
in test-requirements.txt. However, this library is a test
library, so it makes sense for them to be runtime requirements.
As we port other test suites to use oslotest, we can remove
their direct requirement on the tools and let oslotest manage
the version dependency.

Change-Id: I37ccf6514be4fcc21e1954d425e493c7fc920f8c
Merge "Require testrepository and other tools at runtime"