remote-builder: new host isn't ready yet

## Affected builder image

(e.g., `gcr.io/cloud-builders-community/hremote-builder`)

## Expected Behavior

temporary errors SSHing to VM should be handled with retries or another way of verifying that VM is ready should be found

## Actual Behavior

if the VM is not running SSH yet, the SSH fails, thus failing the entire build.

## Steps to Reproduce the Problem

1. run builder as documentation describes
connection refused or invalid key are the messages I've seen. I forked and added a 3 second wait in a 10x retry loop ... the second time it always works.

## Additional Info

I'm running this in a network with some additional configuration, though I am not aware of anything in particular that would slow down instance boot. also got it with the default region. Seems like it's a race condition for everyone to assume that once created, sshd is ready and configured.