[file-asset-apis] Add invalid bucket error handing

[sotojn]

This PR makes the following changes:

File-assets-apis changes

Improvements/Enhancements

• Adds better error handling to when checking to see if a bucket exists
  • Now if checking to see if a bucket exists: It will return false for any status code thats between 400 and 499 with the exception of a 403 code.

File-assets

No changes.

[godber]

A quick comment here after talking with Joseph, I've asked that he keep the 403 error raised like it is with an improvement in the messaging and then I think it's safe to return all other 4xx errors as false.

Then he should document his reference for the implementation of validateBucketName. I think validateBucketName should be exported and used in the user interface validation places. The other functions in s3-helper should just be passing responses from the services through and not introducing even MORE validation on their responses. He should also dig up other S3 compatible services bucket name references. Then we'll consider how to move forward from there.

Also doing some low level testing on ceph to see what it's responses are when given:

• invalid bucket name
• non-existent bucket name