Fix badarg error in couch_os_process
Fix badarg error in couch_os_process

The value of the KillCmd is an iolist and not a
binary, so the binary_to_list call failed.
Issue introduced by COUCHDB-1186.

smithsz/couchdb-couch,fkaempfer/couchdb,ngpestelos/couchdb-couch,cloudant/couchdb-couch,fkaempfer/couchdb,fkaempfer/couchdb,KlausTrainer/couchdb-couch,cloudant/couchdb-couch,fkaempfer/couchdb,alanning/couchdb-couch,KlausTrainer/couchdb-couch,cloudant/couchdb-couch,fkaempfer/couchdb,smithsz/couchdb-couch,ngpestelos/couchdb-couch,KlausTrainer/couchdb-couch,apache/couchdb-couch,apache/couchdb-couch,fkaempfer/couchdb,alanning/couchdb-couch,smithsz/couchdb-couch,alanning/couchdb-couch,ngpestelos/couchdb-couch,apache/couchdb-couch