blkpr: Call gettext() for descriptions, clean up

blkpr: Call gettext() for descriptions, clean up

* Use N_() and _() macros to translate description texts.
* Avoid repeating command/flag/type names in description texts.
* Remove trailing line breaks; it's the caller's task to format
  before/after the descriptions.
* Improve coding style by starting strings at the beginning of the
  line, enhancing maintainability (80 characters limit).
* Keep "}, {" on separate lines as per our usual coding practice.

Signed-off-by: Karel Zak <kzak@redhat.com>