Merge pull request #174 from alphagov/porting-unit-tests-to-rspec-part2

Porting unit tests to rspec (part2)
Port functional tests to rspec
Delete unused rails performance test
Migrate VolatileLock test to rspec
Migrate redirects test to rspec
Spin out rails_helper code into support files
Migrate deduplication test to rspec
Migrate remaining integration tests to rspec