Discovered tonight that some jobs were setting JAVA17 = java1.8.0_last, when the correct value should have been java1.7.0_last.
But on most slaves this variable should be set automatically already; this is probably a relic from a simpler time (when JDK 7 was first being rolled out across the slaves).
So... for the _master jobs, I've removed the parameter. And for the _4.3.mars jobs, I've fixed the parameter.
If both forge and server are still blue in master after this change, we can push the same change into the _4.3.mars jobs AFTER Beta1.