ServiceAccountCredentials.from_json_keyfile_name() ignores token_uri setting in JSON.

[BrandonY]

Steps to reproduce:

1. Generate a service_account.json file.
2. Add a line to JSON file like so:

"token_uri": "https://some-other-auth-uri.website.com/o/oauth2/token",

1. Run this program:

from oauth2client.service_account import ServiceAccountCredentials

def main():
  creds = ServiceAccountCredentials.from_json_keyfile_name('service_account.json')
  print creds.token_uri    # Prints "https://www.googleapis.com/etc"

[theacodes]

@thobrla related to your stuff?

[thobrla]

Yes, #510 should fix this.

[theacodes]

Thanks. :)

[thobrla]

Actually, the pull request will need to be amended to support this specific case (where we get the token_uri from the file). I'll work on that.