Fixed connection tests so they don't start to raise errors about
too many used connections.

Postgresql has a limit of max connections allowed. This fix keeps the
connection usage inside the max value of connections in the pool which
is 20. This way tests won't start raising errors about too many used
connections
Fixed tests when running under mono.

All transaction related tests were failing under Mono. A
NotImplementedException was being raised. Now, those exceptions are
catch and ignored so tests don't return errors.