Fix flaky test in TransactionIT closing socket to terminate transaction.

The test will now allow some time for the socket closing to propagate
network stacks and actually have an effect. It is a speculative fix.
Ability to control maximum number of processors used during import

also made terminology and doc around processor vs. thread in the context
of the importer more clear and consistent.
Merge pull request #3611 from martinfurmanski/2.2-transaction-it-closing-socket-should-terminate-transaction

Fix flaky test in TransactionIT closing socket to terminate transaction.
Merge pull request #3613 from tinwelint/2.2-import-specified-max-threads

Ability to control maximum number of processors used during import