Adding testenv worker wrapper script

Adds a script 60-setup-testenvs which is run by os-refresh-config. On
first boot this carves up the host into a number of test environments
and starts a gearman worker for each environment, noop if run more
than once. Each test environment will have a seed, 3 vm's all on
their own bridge.

Depends-on: Ie33736850ec8186f0c90b82b6fbb0fd57fe47dc9
Change-Id: I46b2c95ccbda484b4de03585b830ac578df0e937
Fix some nitpicks in testenv-work element README

Change-Id: Ibe98e8289f8fcacb21a9b64b141ea9ef0f5c21b6