RFR (XS) 8181450: assert in BasicHashtable::verify_table

[coleen.phillimore at oracle.com]

Summary: remove assert as it has small probability of happening and add 
some logging

Tested new logging with -Xlog:hashtables with failed tests.   See bug 
report for more information.

open webrev at http://cr.openjdk.java.net/~coleenp/8181450.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8181450

Thanks,
Coleen