GRIND-47: Migration tests don't need agent.

Change-Id: I2f34333fe97aa999bd336569575a35ff1127b61b
GRIND-47: Migration testing shouldn't exclude Windows

Change-Id: I5856725a8c6689006562bbbbbfd62d71ce695021
GRIND-47: Allow to boot on specific host.

This will be useful in the next commit.

Change-Id: I28bd47634035dd4f1939cd322ab4e0bdfa7d47d5
GRIND-47: Helper to assert a host supports Cobalt hooks

Change-Id: I68bb3090b1c6425591f108157e40e737fcdd1edd
GRIND-47: Helper to drop a Cobalt hook on a host.

Change-Id: I69767e4c145a2a27eae2933343a7e05d5a3225b3
Merge "GRIND-47: Migration tests don't need agent."
Merge "GRIND-47: Migration testing shouldn't exclude Windows"
Merge "GRIND-47: Allow to boot on specific host."
Merge "GRIND-47: Helper to assert a host supports Cobalt hooks"
Merge "GRIND-47: Helper to drop a Cobalt hook on a host."