supervisor: Add EtcdTable to the test db trigger
supervisor: Add EtcdTable to the test db trigger

When EtcdTable and MinionTable was broken apart, EtcdTable wasn't
added to the trigger in supervisor_test.go.  This caused potential
hangs as database changes wouldn't wake up the test code.

Suggested-by: Kevin Lin <feaf53daf668a750dd729bffb8f8da7a0ce442bf@gmail.com>

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