RFR: 8238599: Refactor and simplify implAddOpensToAllUnnamed

[Claes Redestad]

Hi,

by refactoring implAddOpensToAllUnnamed to take the two sets that
comprise the packages we iterate over, we can make some simplifications,
pre-size HashMaps better etc, adding up to a nice little startup
improvement.

Webrev: http://cr.openjdk.java.net/~redestad/8238599/open.00/
Bug:    https://bugs.openjdk.java.net/browse/JDK-8238599

Testing: tier1+2

Thanks!

/Claes