Produce non-zero exit status on failure using strict

This PR makes `rdlint` return a non-zero exit status when run in `--strict` mode with one or more resource descriptors that produce an error.  This is necessary so that rdlint can be used with Kender.

@miwest929 @sheavalentine-mdsol @brutski 
Would ```exit false``` exit with a status of ```0```?