RFR (XS) 8152380 - Shared symbol/string tables should never use alternate hashcode

[Ioi Lam]

Please review a very small fix:

http://cr.openjdk.java.net/~iklam/jdk9/8152380_shared_table_rehashing.v02/
     https://bugs.openjdk.java.net/browse/JDK-8152380

Summary of fix:

I added a new function, SymbolTable::hash_shared_symbol(), that does not
     use the alternate hashing algorithm.

     To validate the fix, I added new test cases that force alternate 
hashing
     while CDS is enabled (thus we have a shared symbol/string tables).
     Unfortunately the tests are in closed repos.

     Testing showed that the problem existed only for the shared symbol 
table.
     The shared string table already did not use the alternate hashing 
algorithm.

Tests:

     JPRT
     RBT with hotspot tests

Thanks
- Ioi