The ovs_error() function is our standard way of reporting startup errors,
so use it. (It also outputs the program name at the beginning of the
message.)
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.
