bectl(8): Address Coverity complaints

CID 1400451: case 0 is missing a break/return and falling through to the
default case. waitpid(0, ...) makes little sense in the child, we likely
wanted to terminate immediately.

CID 1400453: size argument uses sizeof(char ) instead of sizeof(char *)
and is assigned to a char ; sizeof's match but "this isn't a portable
assumption".

CID: 1400451, 1400453
MFC after: 3 days