Unable to install after previous installation was interrupted

Description of problem:
If you interrupt the installation process during the last phase when EAP is running and run the installer again you are not able to successfully complete the installation.

Version-Release number of selected component (if applicable):
6.0.0 CR2

Steps to Reproduce:
1. Run the installer and proceed to the step where EAP is started for a while.
2. Interrupt the installation by clicking on Quit.
3. Try to run the installer again and see the error messages.

Actual results:
Depends on the time when you interrupt the previous installation the new one either says "The port 9999 is already in use, and is required to be open for this installation." or "The required product.conf or layers.conf file at: .../jboss-eap-6.1/bin/product.conf is missing. Please supply either an empty directory or an EAP installation."

Expected results:
When clicking on the quit button the installer should stop the EAP and clean up the target directory.