STORAGE: Making Connection.get_all_buckets a standalone method.

[dhermes]

See comments in #700 for context.

@tseaver I figured it would be easier to digest moving one method at a time instead of all 4 at once. Still remaining:

$ git grep -e '^    def' -- gcloud/storage/connection.py
gcloud/storage/connection.py:    def __init__(self, project, *args, **kwargs):
gcloud/storage/connection.py:    def build_api_url(self, path, query_params=None, api_base_url=None,
gcloud/storage/connection.py:    def _make_request(self, method, url, data=None, content_type=None,
gcloud/storage/connection.py:    def _do_request(self, method, url, headers, data):
gcloud/storage/connection.py:    def api_request(self, method, path, query_params=None,
gcloud/storage/connection.py:    def get_bucket(self, bucket_name):
gcloud/storage/connection.py:    def create_bucket(self, bucket_name):
gcloud/storage/connection.py:    def delete_bucket(self, bucket_name):
$ git log -1 --pretty=%H
9c783090ea81ec51c6752d24a3637da78a469631

---

NOTE: I re-ran the storage demo to make sure this worked and noticed the very first line was the license. Without the opening

# Welcome to the gCloud Storage Demo! (hit enter)

the demo is pretty tough to use. I can add the license back at the end of the file if necessary or even after # Welcome ... (/cc @jgeewax).

[tseaver]

LGTM. I would just move get_bucket, create_bucket, and delete_bucket in a single PR, though.

[dhermes]

Cool. I'll wait on Travis before merging.

We've also got a 3 PR backup in the "merged" queue:
https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/54143898
https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/54145232
https://travis-ci.org/GoogleCloudPlatform/gcloud-python/builds/54145337

[coveralls]

Changes Unknown when pulling 4f0c483 on dhermes:storage-move-get-all-buckets-to-api into * on GoogleCloudPlatform:master*.

[coveralls]

Coverage remained the same at 100.0% when pulling 4f0c483 on dhermes:storage-move-get-all-buckets-to-api into 39627c0 on GoogleCloudPlatform:master.