make gs_utils.py class-based, so credentials file can be read just once

make gs_utils.py class-based, so credentials file can be read just once

BUG=skia:2618
R=rmistry@google.com

Committed: https://skia.googlesource.com/common/+/b38d520

[epoger, 2014-07-14 15:36:42]

Ravi- Please review at patchset 1.

The Rietveld diff makes this change look bigger than it is.  I have inserted
some notes to help you see what the real changes are.

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py
File py/utils/gs_utils.py (right):

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode46
py/utils/gs_utils.py:46: def __init__(self,
boto_file_path=os.path.join('~','.boto')):
the constructor is new, and includes a chunk of _create_connection from old line
151

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode62
py/utils/gs_utils.py:62: def delete_file(self, bucket, path):
moved from line 43

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode78
py/utils/gs_utils.py:78: def upload_file(self, source_path, dest_bucket,
dest_path):
moved from line 60

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode96
py/utils/gs_utils.py:96: def download_file(self, source_bucket, source_path,
dest_path,
moved from line 79

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode116
py/utils/gs_utils.py:116: def list_bucket_contents(self, bucket, subdir=None):
moved from line 100

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode142
py/utils/gs_utils.py:142: def _create_connection(self):
moved from line 151

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode210
py/utils/gs_utils.py:210: assert dirs == [subdir], '%s == [%s]' % (dirs, subdir)
added more info when asserts fire

[rmistry, 2014-07-14 17:41:50]

LGTM

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py
File py/utils/gs_utils.py (right):

https://codereview.chromium.org/385013004/diff/1/py/utils/gs_utils.py#newcode54
py/utils/gs_utils.py:54: allow the caller to operate on public files.
Nit: Maybe reword this a little-

boto_file_path: full path (local-OS-style) on local disk where .boto credentials
file can be found. An exception is thrown if this file is missing. TODO(epoger):
Change missing file behavior to allow caller to operate on public files.

[epoger, 2014-07-14 17:56:27]

Committed patchset #2 manually as rb38d520 (presubmit successful).