manage_vms needs to be quicker

[jonathanmetzman]

It's slowness is a major source of pain when updating oss-fuzz.
We should give the instance running more cores and make more quota available for it.

[oliverchang]

Another potential bottleneck is rate limits from GCE.

Also, we should get rid of manage_vms completely once we migrate oss-fuzz to the new architecture (and Kubernetes).

[vitorguidi]

Another option is to bring it to terraform, and a kubernetes controller could take over the job of doing the oss fuzz core slicing and host assignment. Good opportunity to decouple business logic from infra management