Teach testenv about numbers and bridges

devtest_testenv is currently not used by toci at all. This is bad,
since the ensure-testenv code is very similar. Start to resolve this
by teaching devtest_testenv about things that toci requires when
setting up test environments.

Change-Id: I3a2fa54498f316748c7361241f3ab5c89038b25f
Merge "Teach testenv about numbers and bridges"