[libmultipath] scope limiting fixes

[libmultipath] scope limiting fixes

I messed up the patch a bit.  Apparently dm_get_uuid() can
return a zero without actually having found a dm name which
matches the name parameter.

Also, I changed dm_get_uuid() so it either returns 1 or a null
string in the uuid return parameter -- in 2 different cases
it was doing neither.

The <dm_device_name> qualifier for the command line
"multipath -ll <dm device name>" can now accept up
to 3 different names for the same dm mapped device,
that is, a user friendly name, an alias in
/etc/multipath.conf, and the current name as
reported by "dmsetup ls".

Edward Goggin, EMC