Refactoring DataSources to use proxy user

Changes
* adding constants for trust id and domain name to swift_helper
* refactoring oozie edp workflows to use proxy configs when necessary
* adding tests to exercise proxy domain usage in workflows
* removing credentials requirement for DataSource models when using
  proxy domain
* pruning duplicate MapReduce test
* adding tests for DataSource creation without credentials
* adding Keystone v3 token endpoint to Hadoop core-site.xml when domain
  requested

Partial-implements: blueprint edp-swift-trust-authentication
Change-Id: I38fd1c470d608c3de9d8c140228d7c9666523b23
Merge "Refactoring DataSources to use proxy user"