Add test case for usage of "flock" tool which demonstrates "write" and "shared" locks

[starnowski]

https://www.putorius.net/lock-files-bash-scripts.html

#1 - write lock first then few shared lock.
Expected: shared locks should failed

#2 - shared lock should be acquired first then write lock then again shared.
Expected: all shared lock should be acquired but the write lock should fail.