p2 director install tests should support install of JBDS from installer, not just BYOE on Eclipse

Max, in JBDS-3485, said:

"I believe the tests all use BYOE install onto JavaEE, not JBDS installer. " that seems very unfortunate and weird since install grinder was written using JBDS to start with.

Can you please make sure we got tests that covers this so we can catch missing pieces like this faster in future ? Thanks.

The p2 director install test [0] uses the same getAndInstallEclipse.groovy [1] mentioned in JBDS-3486 to perform installation of JBT & JBDS discovery site content onto an Eclipse install.

[0] http://jenkins.mw.lab.eng.bos.redhat.com/hudson/view/DevStudio/view/DevStudio_Master/job/jbosstools-install-p2director.install-tests.matrix_master
[1] https://github.com/jbosstools/jbosstools-install-grinder/blob/master/scripts/src/main/groovy/getAndInstallEclipse.groovy

Then, it does this:

${WORKSPACE}/sources/util/installFromCentral.sh -ECLIPSE ${WORKSPACE}/eclipse -INSTALL_PLAN "${INSTALL_PLAN}"

So, it would not be difficult to call a JBDS installer headlessly, then use a different value for -ECLIPSE in the above invocation to install on top of JBDS instead of Eclipse.