Fix error message change in 2.8

Why are we always testing the actual error messages anyway?
Fix adding users in 2.6 and later
getMaster() is blocking, so we only need to wait replication in non-auth mode

awaitReplication() doesn't have permission to tail the oplog in auth mode #fail
10058 is the error code in 2.8
Fallback back to addUser() for 2.4 and 2.2 compatability
The explain output is very different in 2.8
Fixed PHP-1213: Launch mongod with more authenticationMechanisms for testing
dropDups was removed in 2.8
Merge pull request #731 from bjori/2.8-fixes

2.8 test-suite fixes

* bjori/2.8-fixes:
  dropDups was removed in 2.8
  Fixed PHP-1213: Launch mongod with more authenticationMechanisms for testing
  The explain output is very different in 2.8
  Fallback back to addUser() for 2.4 and 2.2 compatability
  10058 is the error code in 2.8
  getMaster() is blocking, so we only need to wait replication in non-auth mode
  Fix adding users in 2.6 and later
  Fix error message change in 2.8