GCSMap fails when we don't have strong permissions about gcsfs HOT 3 CLOSED

It looks like this boils down to this:

>>> fs.ls('pangeo-data')
['pangeo-data/newmann-met-ensemble-netcdf/',
 'pangeo-data/newmann-met-ensemble/']
>>> fs.exists('pangeo-data')
ValueError

from gcsfs.

Hm, doing exists(bucket) is problematic if it doesn't show up as one of your buckets. Perhaps there should be a fallback to listing the bucket.
In fact, testing for the bucket isn't necessary at all if you only ever read, it could be removed, and then you would defer the error to access time if the bucket really doesn't exist.

from gcsfs.

Right, _list_buckets should probably return [] if you don't own any buckets, and if the bucket is not found in that list, exists(bucket) should try ls(bucket) and return True if that succeeds (even if the bucket is empty).

from gcsfs.