There's an inconsistency between chasquid (which uses `--config_dir`) and
chasquid-util (which uses `--configdir`).
That is prone to cause confusion, so this patch renames chasquid-util's
flag, leaving the old one as deprecated with a warning message.
Closes https://github.com/albertito/chasquid/pull/60.
Amended-by: Alberto Bertogli <albertito@blitiri.com.ar>
Added test case for the deprecated option, adjusted commit message.
