Add a custom CLI module for DataCollectors

Currently, the mon-collector binary uses the HTools/CLI module, which
is OK but mean it links in lots of htools code. By copying that module
to DataCollectors/CLI and removing the unneeded code, we reduce the
number of modules it depends on fro 20 to 12, meaning both a shorter
compiler time (24s to 9s) and a smaller binary (~9.6MB to ~7MB).

Also fixes a typo in the original HTools/CLI module, thanks Michele!

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>