[8u-dev] RFR - 8156824: com.sun.jndi.ldap.pool.PoolCleaner should clear its context class loader

[Rob McKenna]

Hi folks,

I'd like to backport this change to 8u-dev.

The changes are straightforward enough but 8u needs some changes that
were made to InnocuousThread. (strictly it doesn't need all of the
changes I've made but I've made an effort to make the code look as close
to 9 as possible)

bug: https://bugs.openjdk.java.net/browse/JDK-8156824
9u changeset: http://hg.openjdk.java.net/jdk9/jdk9/jdk/rev/22e704dfa05c
8u webrev: http://cr.openjdk.java.net/~robm/8156824/webrev.01/

    -Rob