Due to some limitations in Python ( see https://bugs.python.org/issue9338 ) the current setup with -c that accept an optional value doesn't allow to use it as the only or last parameter.
These invocations will fail with the unhelpful message too few arguments:
wmf-auto-reimage -c hostname wmf-auto-reimage -a -c hostname
While these will work
wmf-auto-reimage -c -- hostname wmf-auto-reimage hostname -c wmf-auto-reimage -c -a hostname
This limited behaviour should be documented and if possible also catch the unhelpful error and print a better error message in case -c was specified.