Use EXIT_SUCCESS and EXIT_FAILURE

Instead of randomly using -1 or 1 as a failure status, properly utilize
the EXIT_FAILURE define that's platform specific (as it should be).

bin/dnssec/dnssec-importkey.c

@@ -289,7 +289,7 @@ usage(void) {
 	fprintf(stderr, "    -D sync date/[+-]offset/none: set/unset "
 			"CDS and CDNSKEY deletion date\n");
 
-	exit(-1);
+	exit(EXIT_FAILURE);
 }
 
 int
@@ -395,7 +395,7 @@ main(int argc, char **argv) {
 		default:
 			fprintf(stderr, "%s: unhandled option -%c\n", program,
 				isc_commandline_option);
-			exit(1);
+			exit(EXIT_FAILURE);
 		}
 	}