treewide: drop use of which

treewide: drop use of which

Ubuntu started to flag which as deprecated and it
seems which is not really standard and may vary
across Distro.
Drop the use of which and use the standard 'command -v'
for this simple task.
Which is still present in the prereq if some package/script
still use which.
A utility script called command_all.sh is implemented that
will just mimic the output of which -a.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>