RFR: 8014508: Fix log levels in make

[Erik Joelsson]

in JDK-8010465, an attempt was made to clear up log level handling. It 
wasn't completely successful. The log level isn't available to sjavac 
and probably not in several other places that needs it.

I solved it by adding LOG_LEVEL=$(LOG_LEVEL) to the MAKE variable in 
spec.gmk, much like the VERBOSE variable is propagated.

http://cr.openjdk.java.net/~erikj/8014508/webrev.root.01/

/Erik