chore(storage): add multi-transport test runner (#6639)
chore(storage): add multi-transport test runner (#6639)

Introduces a `multiTransportTest` runner that executes a given test function with each transport-specific client library, HTTP/JSON and gRPC. This also migrates a few tests that worked OOTB as PoC. Each test should be migrated individually so that any fixes necessary can be made in the same PR (there will be some, I already experienced a few). 

Removes an unnecessary `-` suffix from the gRPC test bucket name prefix used to create the `uid` generator for gRPC.

Switches `uid` generators into `Short` mode to keep names under the 63 character bucket name limit.
googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go