Pass node to various Build*() functions

Pass node directly from XML to these functions

- BuildClusterImage()
- BuildImage()
- BuildProxy()
- BuildRunTests()

instead of reading the "server ID" and looking up from
eNB_IPAddress/eNB1_IPAddress/eNB2_IPAddress.

Improve the proxy build unit test by properly passing ctx information.

ci-scripts/xml_files/cluster_image_build.xml

@@ -37,6 +37,7 @@
 	<testCase id="000001">
 		<class>Build_Cluster_Image</class>
 		<desc>Build Images on OpenShift Cluster</desc>
+		<node>poseidon</node>
 	</testCase>
 
 </testCaseList>