Use the event handler to capture stderr, stdout for python.

Cleaned up test suite infrastructure a bit using this.
Any verbose messages from the infrastructure itself do not get captured.
refs WT-649

test_reconfig.py needed special treatment. Verbose output from
threads is not necessarily flushed until the connection is closed;
we reopen the connection to force the flush so that the test should
pass on all platforms.
refs WT-698