Describe the failure.

These matchers look at the console output, so better to just dump them
Fixing an assertion.

On my Ubuntu 12.04, vncserver is tightvnc, so the output looks like the following:

    Terminating xvnc.
    $ vncserver -kill :77
    Killing Xtightvnc process ID 7868
    Finished: SUCCESS

Since vncserver output is fragile, It's better to assert on the output from the plugin.