Work stealing for non partition specific operation threads.

Each non partition specific thread had a private queue, but now they have a shared queue so
that it doesn't happen that an operation is pending even though there are free generic
operation threads.
Refactor map eviction manager code. (Hold references of key-value pairs not Record objects)
Merge pull request #2325 from pveentjer/improvement/3.x/opservice-workstealing-nonpartitionthreads

Work stealing for non partition specific operation threads.
Merge pull request #2326 from ahmetmircik/ms/fix2324

Fixes #2324