qemu.tests.cfg: Add umount_cmd config for format_disk test

And add quote mark for config parameters.
Signed-off-by: NQingtang Zhou <qzhou@redhat.com>

qemu/tests/cfg/format_disk.cfg

@@ -6,14 +6,15 @@
     image_name_disk1 = images/storage
     image_size_disk1 = 10G
     force_create_image_disk1 = yes
-    writefile_cmd = echo
     kill_vm = yes
     cmd_timeout = 1200
     # The following parameters will be overriden in guest-os config files.
     create_partition_cmd = ""
-    format_cmd = cd /dev && for i in `ls | egrep [shv]db`;do yes |mkfs.ext3 $i; done
+    format_cmd = "cd /dev && for i in `ls | egrep [shv]db`;do yes |mkfs.ext3 $i; done"
     list_disk_cmd = ""
     set_online_cmd = ""
-    mount_cmd =  cd /dev && ls | egrep [shv]db | xargs -I dev mount -t ext3 dev /media
-    testfile_name = /media/txt.txt
-    readfile_cmd = cat
+    mount_cmd =  "cd /dev && ls | egrep [shv]db | xargs -I dev mount -t ext3 dev /media"
+    umount_cmd = "mount | grep -Eo '/dev/[shv]db' | xargs umount"
+    testfile_name = "/media/format_disk-test.txt"
+    writefile_cmd = "echo"
+    readfile_cmd = "cat"