tools: add checkusage.sh

tools: add checkusage.sh

Just some simple generic tests for our UL commands, regarding
options --help, --version and --unknownopt.

The script looks still a bit weired but could be polished to
be used in tests/. It would be the first time testing at least
"something" for *all* built binaries (currently 109! commands).

For the record here are the current candidates with possible
problems:

$ make checkusage
agetty: --unknownopt, stderr too long: 45
blockdev: --unknownopt, stderr too long: 28
flock: --help, no stdout
flock: --help, non-empty stderr
getopt: --help, returns error
kill: --unknownopt, stderr too short: 1
lsipc: --unknownopt, stderr too long: 77
pg: --unknownopt, stderr too long: 23
renice: --unknownopt, stderr too long: 18
rtcwake: --unknownopt, non-empty stdout
rtcwake: --unknownopt, stderr too long: 21
sulogin: --unknownopt, stderr too long: 17
write: --unknownopt, stderr too long: 12

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>