RFR: 8010465: Can't enable sjavac when building in jprt.

[Erik Joelsson]

This patch makes it possible to enable sjavac in jprt runs. This is 
achieved by adding -buildenv ENABLE_SJAVAC=true to the jprt command line.

http://cr.openjdk.java.net/~erikj/8010465/webrev.root.01/

Doing this uncovered another bug. Adding the keyword "nofile" to the LOG 
variable is done to disable logging build output to a file. JPRT does 
this on all build runs since it already saves the build output. The 
value of LOG is also sent to sjavac to help it filter its output, but 
sjavac does not accept "nofile" as input. The logic to remove "nofile" 
before sending it to sjavac didn't work and is also fixed in this patch.

The sad news is that all the windows builds currently fail with sjavac 
enabled, but having this feature will help us harden sjavac to the point 
where we can make the switch.

/Erik