RFR: 8159334: ModuleDescriptor retains overlapping sets for all and concealed packages

[Claes Redestad]

Hi,

please review this patch to remove the set of concealed packages from 
ModuleDescriptor and instead only calculate it on demand.

Webrev: http://cr.openjdk.java.net/~redestad/8159334/webrev.01/
Bug: https://bugs.openjdk.java.net/browse/JDK-8159334

The conceals() method is currently used primarily by tools (jmod, 
jlink), but never during startup or normal execution.  Removing creation 
of it drops around 35Kb of heap data from a hello world program (on a 
JDK image) as well as giving a small improvement to startup time by 
virtue of creating fewer sets during bootstrap.

Thanks!

/Claes