Fixed broken test. Get parameters should be used to make to the signature.

http://oauth.net/core/1.0a/#anchor13
9.1.1.  Normalize Request Parameters
The request parameters are collected, sorted and concatenated into a normalized string:
HTTP GET parameters added to the URLs in the query part (as defined by [RFC3986] section 3).
Removed duplicate code for getting params to sign.
Made optional params only be signed if they have been set in the config, and not null by default.
Added test to check that optional params have not been added if they were not set in the config for the OauthPlugin.
Fixed issue where request params were being copied to the Authorization header.
Reverted test to remove incorrect strings, but left order be flexible.
Spelling typo.
Merge remote-tracking branch 'danack/OauthOptionalVariables'
CS cleanup