Log Message:
Update py-gsutil to 4.31.

Fix all dependencies. This time, there is an actual working gsutil binary.
Thus, fix PR pkg/52941.

Release 4.31 (release date: 2018-04-26)
=======================================
New features
------------------
- Added support for reauthentication within gsutil. Note that this only affects
  authentication when "gs_oauth2_refresh_token" is configured under the
  "Credentials" section of the boto config file and that token \ 
corresponds to a
  user account enrolled in 2-step verification.

Bug Fixes
------------------
- When creating a signed URL via the "signurl" command, gsutil now \ 
verifies that
  the specified expiration isn't longer than 7 days (the maximum allowed by the
  service).
- To support rewriting objects to be encrypted using a bucket's default KMS key,
  the "rewrite" command now rewrites all specified objects if no value is
  specified for "encryption_key" under the "GSUtil" section \ 
in the boto config
  file.

Other Changes
------------------
- Several documentation updates and clarifications.

Release 4.30 (release date: 2018-03-28)
=======================================
New features
------------------
- Added Cloud KMS support for Google Cloud Storage resources, allowing the use
  of customer-managed encryption keys (CMEKs). Bucket-related functionality
  includes the new "kms" command, which can be used to get or set a \ 
bucket's
  default KMS key. Concerning objects, users may now specify the CMEK to be used
  for encryption via their boto config file, in the "encryption_key" \ 
attribute.
  In this way, users may specify either a CSEK or a CMEK to encrypt new objects,
  but not both. For more information, see "gsutil help encryption".

Other Changes
------------------
- Several documentation updates and clarifications.

Release 4.29 (release date: 2018-03-14)
=======================================
New features
------------------
- Added transport compression support, available through the "-j" and \ 
"-J"
  options for the "cp", "mv", and "rsync" \ 
commands. This is useful when
  uploading files with highly-compressible content. When specificed, files being
  uploaded are compressed on-the-fly in memory, sent to GCS, and uncompressed by
  GCS before they are stored. See "gsutil help cp" for additional \ 
information.
- When "use_magicfile=True" is set in the boto config file, gsutil will now
  append the detected charset, if present, to the object's Content-Type metadata
  field. For example, a Content-Type might be populated with
  "text/html; charset=us-ascii" rather than simply "text/html".

Bug Fixes
------------------
- Improved error handling and logging for upload resumption.
- After encountering a PreconditionException, the "acl ch" command will now
  re-fetch the object generation before retrying.
- Fixed issue with parsing lifecycle conditions when using the XML API.
  Conditions whose values could be evaluated by Python as "falsy" \ 
(e.g. setting
  an "age" condition to the number 0 or "isLive" to false) \ 
would be omitted from
  the lifecycle configuration when "prefer_api=xml" was set in the \ 
boto config
  file. Note that the JSON API is preferred by default, so most users were
  unlikely to encounter this issue.
- For commands that fetch bucket ACLs or default ACLs, when the user does not
  have storage.buckets.getIamPolicy on the GCS bucket, using the XML API will
  now behave consistently with the JSON API and display ACL/default ACL fields
  as empty, rather than throwing a CommandException.

Other Changes
------------------
- Several documentation updates and clarifications.
- The "signurl" command now uses signature V4 signing format to \ 
generate URLs.