TPU Provisioner: Fix skipped scale ups & garbage collect zombie node pools

[nstogner]

• Avoid scale ups when node pool is in a deletion state.
• Avoid scale ups when the Pod being reconciled is in a deletion state.
• Use owner UID for node pool names to avoid scale up failure when the scheduler has placed another workload on the same existing node pool.
• Run a loop that deletes node pools that have no Nodes, are in an errored state, and where the Pod that created the node pool no longer exists (the deletion reconciler would not see these b/c there are no Node objects).
• Update events to be more descriptive for easier debugging.
• Make Secure Boot configurable (defaults to same behavior).
• Make deletion delay configurable to ensure make test passes consistently.

[danielvegamyhre]

LGTM overall, left a few minor comments and questions

[nstogner]

Updated to address comments. Also made deletion delay configurable to make sure make test passes consistently.

[nstogner]

Rebased @danielvegamyhre

[danielvegamyhre]

/gcbrun