This change turns off fsync on the postgres container used for tests. This
reduces migration time significantly when initializing new satellite
databases.
The change also includes a new benchmark for satellite initialization in
testplanet.
$ benchstat old.txt new.txt name old time/op new time/op delta
Run_Satellite/Postgres-16 1.36s ± 0% 0.08s ± 0% ~ (p=1.000 n=1+1)
Change-Id: Ic954767133864770cf652b0dfdcd6b109a167b5f