libdm: add dm_task_get_uuid_mangled/unmangled

libdm: add dm_task_get_uuid_mangled/unmangled

Just like we already have existing mangling support for
device-mapper names, we need exactly the same for device-mapper
UUIDs as their character whitelist is wider than what udev supports.

In case udev is used to create entries in /dev based on UUIDs
and these UUIDs contain characters not supported by udev,
we'll end up with incorrect /dev content for such devices.
So we need to mangle them to a form that is supported by udev.

The mangling used for UUIDs follows the mangling used for names
(that is already supported and used throughout). That means,
setting the name mangling mode via dm_set_name_mangling_mode
affects mangling used for UUIDs in exactly the same manner.
It would be useless to add a new and separate
dm_set_uuid_mangling_mode fn, we'll reuse existing interface.