RFR: 8014510: Fix sjavac on all platforms in jprt

[Andreas Lundblad]

Hi build-dev,

Please review the fix for JDK-8014510: Fix sjavac on all platforms in jprt

Description:
JPRT jobs fail (on Sparc) with sjavac enabled. This is because the JVM can't allocate the requested amount of memory upon launch. This patch changes the the -Xms setting (which ranges from 1G to 10G) to 512M.

Link to webrev:
http://cr.openjdk.java.net/~alundblad/8014510

Links to bug report:
https://bugs.openjdk.java.net/browse/JDK-8014510

-- Andreas