RFR JDK-8039525: HashTable lookup API needs refactoring

[Gerard Ziemski]

hi all,

Please review this simple enhancement, which renames symbolTable::lookup 
API using names that better reflect the method purpose, ie: lookup_only, 
lookup_and_add, lookup_only_and_hash, lookup_and_add_unicode and 
lookup_only_and_hash_unicode.

No new or removed code.

Webrev: http://cr.openjdk.java.net/~gziemski/8039525_rev0
Bug: https://bugs.openjdk.java.net/browse/JDK-8039525

Tested with hotspot jtreg, vm.quicklooks and JPRT. Locally builds on Mac 
OS X and Linux.

Thank you.