common: fix "utility required warning" with empty utility name

In generic/019, if we hadn't install fio, we will get following output:

 generic/019      [not run]  utility required, skipped this test <- *
 Not run: generic/019
 Passed all 0 tests

When fio is not installed, "$FIO_PROG" is set to blank, and
_require_fio() call _require_command() with none arguments.

This patch fixed all misuse of _require_command(), add 2nd argument
to let _require_command() output right message, and add quotes to
first argument to avoid argument shifting.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

common/rc

@@ -1299,7 +1299,7 @@ _require_dm_flakey()
 {
     # require SCRATCH_DEV to be a valid block device
     _require_block_device $SCRATCH_DEV
-    _require_command $DMSETUP_PROG
+    _require_command "$DMSETUP_PROG" dmsetup
 
     modprobe dm-flakey >/dev/null 2>&1
     $DMSETUP_PROG targets | grep flakey >/dev/null 2>&1
@@ -2289,7 +2289,7 @@ _require_deletable_scratch_dev_pool()
 _require_btrfs()
 {
 	cmd=$1
-	_require_command $BTRFS_UTIL_PROG btrfs
+	_require_command "$BTRFS_UTIL_PROG" btrfs
 	if [ -z "$1" ]; then
 		return 1;
 	fi
@@ -2302,7 +2302,7 @@ _require_fio()
 {
 	job=$1
 
-	_require_command $FIO_PROG
+	_require_command "$FIO_PROG" fio
 	if [ -z "$1" ]; then
 		return 1;
 	fi