Rewrite or remove testcases/kernel/fs/doio/rwtest

[pevik]

testcases/kernel/fs/doio/rwtest is very old script written in bash. Decide if it's still useful, if yes, then rewrite it to new C or shell API otherwise delete.

Also its usage in the runtest/fs is very ugly.

rwtest01 export LTPROOT; rwtest -N rwtest01 -c -q -i 60s  -f sync 10%25000:$TMPDIR/rw-sync-$$
rwtest02 export LTPROOT; rwtest -N rwtest02 -c -q -i 60s  -f buffered 10%25000:$TMPDIR/rw-buffered-$$
rwtest03 export LTPROOT; rwtest -N rwtest03 -c -q -i 60s -n 2  -f buffered -s mmread,mmwrite -m random -Dv 10%25000:$TMPDIR/mm-buff-$$
rwtest04 export LTPROOT; rwtest -N rwtest04 -c -q -i 60s -n 2  -f sync -s mmread,mmwrite -m random -Dv 10%25000:$TMPDIR/mm-sync-$$
rwtest05 export LTPROOT; rwtest -N rwtest05 -c -q -i 50 -T 64b 500b:$TMPDIR/rwtest01%f