Adding 429 retry in storage for bucket create and delete.

[dhermes]

Showed up when Travis when 3 merge builds right on top of each other:

https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/154249353
https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/154251510

@tseaver I am trying to force the failure locally so I can see more fine-grained error info but 429 is pretty specific so I'm not that worried. I also would like to add a debug flag so we get more error info in our failure messages on Travis.

[dhermes]

(Pdb) print(content)
{
"error": {
"errors": [
{
"domain": "usageLimits",
"reason": "rateLimitExceeded",
"message": "The project exceeded the rate limit for creating and deleting buckets."
}
],
"code": 429,
"message": "The project exceeded the rate limit for creating and deleting buckets."
}
}
(Pdb) print(json.dumps(response, indent=2))
{
"status": "429", "alternate-protocol": "443:quic", "content-length": "301", "x-xss-protection": "1; mode=block", "x-content-type-options": "nosniff", "transfer-encoding": "chunked", "expires": "Mon, 22 Aug 2016 21:10:37 GMT", "vary": "Origin, X-Origin", "server": "GSE", "-content-encoding": "gzip", "cache-control": "private, max-age=0", "date": "Mon, 22 Aug 2016 21:10:37 GMT", "x-frame-options": "SAMEORIGIN", "alt-svc": "quic=\":443\"; ma=2592000; v=\"35,34,33,32,31,30\"", "content-type": "application/json; charset=UTF-8"
}
(Pdb) exc=make_exception(response, content, error_info=method+' '+url)
(Pdb) print(json.dumps(exc.errors, indent=2))
[
{
"reason": "rateLimitExceeded", "domain": "usageLimits", "message": "The project exceeded the rate limit for creating and deleting buckets."
}
]

[tseaver]

pylint is unhappy.

[tseaver]

LGTM once pylint is appeased.