RFR: 8014508: Fix log levels in make

[Tim Bell]

Erik:

> 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

Looks good.

Tim