Move all devtest actions into child scripts.

This makes it possible to use them independently rather than running
the entire devtest all at once. There are other changes we might want
to do to the scripts, but since there is a lot of text moving I've
been conservative - we can do other changes in subsequent patches.

Change-Id: I6522d9443bcdbc1ae16b485ae3b9d8e547a6022f
Consolidate VM creation into devtest_setup.sh.

To run CI tests we have to use predefined baremetal nodes rather than
creating them during the test script - they might be real hardware, or
the virtual test clusters. Separating out creation from use also
permits tweaking the test VMs by hand, which can be a useful debugging
feature.

Change-Id: I698841b7beb4a2f847405664f46805ea7be4dc53