Fix BrooklynEntityMirror tests
Fix testSecurityProviderUpdatesWhenPropertiesReloaded

- was failing for me because my brooklyn.properties has authentication
  set up. Therefore set an explicit brooklynProperties just for
  the test.
Fix REST api testGetUser

- we were getting the `user` too early, before the 
  AUTHENTICATED_USER_SESSION_ATTRIBUTE had been set.
MongoDB router cluster: rename param
docs/start/download.md: apache-nexus-snapshots repo
BrooklynLauncherRebindToCloudObjectStoreTest: minor improvement

- FIXME comments about failures seen in jenkins
- mark setUp() as alwaysRun=true
This closes #244