Fix building script for sh shell

Fix for problem described below:
crackers 1:30 PM frohike: you have some error in the code in m_unix.... an extra [[ somehere
crackers 1:47 PM jl777: updated and restarted all my nodes
frohike 3:06 PM @crackers  it works over here. You got a line number?
frohike 3:26 PM I know it already
it's bash typical, and the script is bourne shell compatible.
which is better.
So, I rewrite those lines with a normal if conditional.