TriggerRemoteBuildsTest fixes and more

Simplified security setup by using the GlobalSecurityConfig
page object. A new ServletSecurityRealm was added for this
purpose.
Uses BuildHistory to verify the number of builds.

Using open() instead of visit() in Slave.java

Change-Id: Ie8809076faa9f041395a48a2a4dc043ac2f89012
Merge branch 'm'