To reduce the total number of invocations necessary for pip which isn't
the quickest thing ever (due to needing to evaluate constraints and deps
lists and what is currently installed) combine the main installation of
software with its test-requirements.txt file which should roughly halve
our pip invocations.
Change-Id: Ibcc3264136e66d34a879ad1c90a62e1bb6a84243
f266a2dc81