Changed python test suite to allow for shorter runs by default,
with a --long (or -l) option for the complete runs.  Txn02 in particular
now runs only a small number of scenarios by default.  Also added a
@longtest("description") decorator for individual tests that can be
marked to be run only under --long.  Refs #1461.
Allow pruning scenarios with different limits for default vs. long runs.
The pruned scenario list now matches the original ordering.
Tests now print with both the scenario number and the scenario args.
This should make it easier to diagnose and debug problems that effect
only certain scenarios.  Refs #1461.
Used prune_scenario limit the number of scenarios for default test runs.
Refs #1461.
Merge pull request #1464 from wiredtiger/testsuite-long

Changed python test suite to allow for shorter runs by default.