Pull cord-tester images from dockerhub as they are available now on dockerhub.
Change image names to be compatible with dockerhub image names.
Update prerequisites.sh last step to pull all the cord-tester docker images.
This should make the cord-test.py build all step redundant now since images should be available for testing immediately after prerequisites.sh are run.

Change-Id: I64cf664a214924349d6728ca2a52974decdef47f
diff --git a/Dockerfile.tester b/Dockerfile.tester
index 966f45b..efbf359 100644
--- a/Dockerfile.tester
+++ b/Dockerfile.tester
@@ -7,7 +7,7 @@
         python python-pip python-setuptools python-scapy tcpdump doxygen doxypy wget \
         openvswitch-common openvswitch-switch \
         python-twisted python-sqlite sqlite3 python-pexpect telnet arping isc-dhcp-server \
-        python-paramiko python-maas-client
+        python-paramiko python-maas-client python-keystoneclient python-neutronclient python-glanceclient
 RUN easy_install nose
 RUN mkdir -p /root/ovs
 WORKDIR /root