Change 'oauth_extension' to 'oauth1_extension'

The documentation uses 'oauth1_extension' but the configuration files
an tests use 'oauth_extension'. This change sets all of them to
oauth1_extension.

Closes-Bug: #1275693
Change-Id: I279f08e262d6f1ae8afea58fd46576e3eabf3875
DocImpact: Extension name has been changed in keystone-paste.ini,
therefore the pipeline may need to be adjusted as well
Merge "Change 'oauth_extension' to 'oauth1_extension'"