Add support for modes.

There are now three operation modes, any number of which can be active
at one time:

* :offset - the ports will be offset by 100
* :isolated - the AS will have isolated log and data dirs
* :lazy - an existing server will be used if it is running. The server
  that we look for is determined by the :offset mode.

The default mode set is: #{:isolated :offset}

No matter what modes are selected, any AS started by fntest will now
have its filesystem-based deployer disabled.
Release 0.4.1.
Bump version to 0.4.2-SNAPSHOT.