Change the way the result from a command is reported. Instead of separate

Change the way the result from a command is reported.  Instead of separate
ev_varnish_command_ok and ev_varnish_command_unknown events, we now emit
a single ev_varnish_result event accompanied by the result code and text.
Furthermore, Varnish::Test::Varnish::send_command() will now wait for this
event and return the code and text.

Note that this reintroduces a race between ev_varnish_child_stopped and
ev_varnish_result; this will be dealt with in a later commit.

git-svn-id: svn+ssh://projects.linpro.no/svn/varnish/trunk@1864 d4fa192b-c00b-0410-8231-f00ffab90ce4