Correctly prefix storage emulator routes

[jcmorrow]

Description

Hello! This is my attempt at a bug-fix, I don't think there are related issues, but there might be. I sunk like six hours into figuring this out yesterday, and of course the fix turned out to be a change of ~10 characters. Let me give some context as to how I got here:

• I am working on an application that hits the storage API at start-up time, and I wanted to spin up local emulators so that new devs wouldn't need to have a fully-set-up cloud project just to run a local server.
• I got the local emulator running, interacted with it via the WebUI, confirmed that it was working, but when I tried to list the buckets, or list objects in a particular bucket from my Go code, it failed.
• With a bit of digging, I realized that it was failing because the server was returning 501 not implemented.
• I decided to take a different tack, since in the docs of the client library it mentions that buckets are implicitly created upon writing an object in them. I decided to try and write an object to a bucket, and that created the bucket just fine, I could see it in the webUI and everything. You can see me live debugging this a bit on the Slack
• Anyways, long story short, I dug into the code this morning and saw that some of the routes for the storage emulator are prefixed with /storage/v1 and some are not.
• The Go client library explicitly sets that prefix as the root path: https://github.com/googleapis/google-cloud-go/blob/0e7ccf1cc95c84838cc3de722ff4cc2e5098f579/storage/storage.go#L143. I don't know if the other client libraries do this, but it seems reasonable, since all of the documentation includes that prefix.
• I don't see any tests that cover how routes link up to actions, so I'm not adding anything here, but I've confirmed that this works with the Go client library as expected.

Scenarios Tested

• Creating a bucket from the Go client library without creating an object inside of it, as in this example: https://github.com/GoogleCloudPlatform/golang-samples/blob/master/storage/buckets/create_bucket.go
• Listing buckets from the Go client, as in this example: https://github.com/GoogleCloudPlatform/golang-samples/blob/master/storage/buckets/list_buckets.go

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[jcmorrow]

@googlebot I signed it!