Rename quickstarts directory to GA

Since installer is not part of neither alpha nor beta release, we can use GA name for quickstarts target directory.

Reproduce:
Install quickstarts into ${QS_TARGET} directory
Actual:
${QS_TARGET}/jboss-eap-7.1.0.DR2-quickstarts
Expected:
${QS_TARGET}/jboss-eap-7.1.0.GA-quickstarts

Please come up with some more robust solution so we avoid this issue in future releases.