JDK-8027113 fix for jdk 9 code review

[Ron Durbin]

JDK-8027113 decouples the '-XXaltjvm=<path>' option from the gamma launcher


Web URL http://cr.openjdk.java.net/~rdurbin/JDK-8027113-cr1-webrev

Internal URL: http://javaweb.us.oracle.com/~rdurbin/JDK-8027113-cr1-webrev

Summary:
Refactor the code so that it is no longer tightly coupled with the "gamma launcher". This will allow work on the following bug to proceed:

    JDK-8005262 possible gamma launcher issues 

Testing included:
 JPRT run
 Manual launcher tests on Solaris 64 bit, Linux 64 bit.