The current mechanism for adding plugins to the integTest cluster is to
have a FileCollection. This works well for the integTests for a single
plugin, which automatically adds itself to be installed. However, for qa
tests where many plugins may be installed, and from other projects, it
is cumbersome to add configurations, dependencies and dependsOn
statements over and over. This simplifies installing a plugin from
another project by moving this common setup into the cluster
configuration code.