extract get_session method on claim
update to active with contention returns 409
release inactive lock returns 409
remove duplicate promote_resource code
claim release does not activate other claims
remove unused expire method
simplify Claim.release
remove impossible branch
clarify switch-case style code statement
remove user_data serialization error check

We cannot make this failure occur since the user data was already
serialized JSON when it was passed through the request.
Merge pull request #20 from mark-burnett/cleanup-branch-coverage

Cleanup branch coverage
Merge pull request #19 from mark-burnett/refactor-to-promote-lock

Refactor to promote lock