mke2fs: Deprecate -K option, introduce discard/nodiscard

mke2fs: Deprecate -K option, introduce discard/nodiscard

It would be nice to have consistent "discard" options in every system
tool (mount, fsck, mkfs) taking advantage of discards. Also "discard"
and "nodiscard" is more descriptive instead of just "-K" and can be
easily defaulted and it is something we can not do with "-K".

With this commit you need to specify extended option like this:

./mke2fs -T <fstype> -E nodiscard <device>

in order make a filesystem without discarding the device first. And

./mke2fs -T <fstype> -E discard <device>

respectively.

-K option is with this commit deprecated and should not be used anymore.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>