Sanitize cluster names / make names with underscores be able to run on GCP

[concretevitamin]

multi_echo.py was using the cluster name multi_echo. When forcing it on GCP, it failed with

googleapiclient.errors.HttpError: <HttpError 400 when requesting https://compute.googleapis.com/compute/v1/projects/intercloud-320520/zones/us-west1-a/instances?alt=json returned "Invalid value for field 'resource.name': 'ray-multi_echo-head-480dea0e'. Must be a match of regex '(?:a-z?)'". Details: "[{'message': "Invalid value for field 'resource.name': 'ray-multi_echo-head-480dea0e'. Must be a match of regex '(?:a-z?)'", 'domain': 'global', 'reason': 'invalid'}]">

Replacing the name with multi-echo worked. It must be regex (?:[a-z](?:[-a-z0-9]{0,61}[a-z0-9])?)

Need to design a solution (force replace _ with -? some other approach?).

[gmittal]

Related: sky gpunode 42 will fail because 42 is not a string, but then its also not removable from the status table because of the same problem.