to prevent cascading errors. Clean up and (mostly) standardize how connection
configuration is added to and modified.
Details:
- class TestSuiteConnection wraps an opened Connection,
calls to close() remove it from the list of active connections.
- WiredTigerTestCase.wiredtiger_open uses a TestSuiteConnection, and this
version of wiredtiger_open is now used everywhere.
- in tearDown(), active connections are explicitly closed.
- In WiredTigerTestCase derived classes, we now use use self.conn_config
if possible in tests in preference to overloading setUpConnectionOpen().
- Explicitly call close on extra connections created dynamically.
- Remove some unused code.
