I started working on a new command line utility that used this shared
code.  I wanted the ability to pass some data from common
initialization code to all of the commands.  You can find a similar
pattern in ovs-vsctl.

This patch updates the command handler to take a new struct,
ovs_cmdl_context, instead of argc and argv directly.  It includes argc
and argv, but also includes an opaque type (void *), where the user of
this API can attach its custom data it wants passed along to command
handlers.

This patch affected the ovstest sub-programs, as well.  The patch
includes a bit of an odd hack to OVSTEST_REGISTER() to avoid making
the main() function of the sub-programs take a ovs_cmdl_context.
The test main() functions still receive argc and argv directly, as
that seems more natural.  The test-subprograms themselves are able to
make use of a context internally, though.

Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>