It is inconvenient to type the whole path to the Unix daemon socket when
using ovs-appctl.  Allow the name of the daemon to be used instead when
a pidfile exists in the default location, and contact ovs-vswitchd by
default.

Also, the various options for manipulating vlog were invented before the
general-purpose command mechanism existed.  Get rid of all of the action
options in favor of just specifying the command to be executed as
non-option arguments.

Finally, there simply wasn't much value in allowing multiple targets or
options to be specified; these variations were never used in practice.  So
simplify the interface by making it one target, one action per invocation.

Also, make ovs-vsctl use the same syntax for its --target option.

Based on work by Justin Pettit.