configurable cluster.adminname, cluster.password

provide option to set cluster.adminname and cluster.password in the
build.xml test related properties section.

Change-Id: I46c2e595ed16d477bbd09062cf554c7df2915928
Reviewed-on: http://review.couchbase.org/33137
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>