parallels: add VIR_STORAGE_FILE_PLOOP format

Add VIR_STORAGE_FILE_PLOOP format. This format is used
to store disk images for virtual machines in PCS and containers
in PCS, OpenVZ and also in Parallels Desktop for Mac.

This format is described on OpenVZ site -
https://openvz.org/Ploop (together with ploop devices). It
consists of XML descriptor and one or more image files: base
image and deltas. Format of the image files described here:
https://openvz.org/Ploop/format.

This patch only adds VIR_STORAGE_FILE_PLOOP constant, consequent
patches will use it in parallels driver.

Signed-off-by: Dmitry Guryanov <dguryanov@parallels.com>

src/util/virstoragefile.c

@@ -62,7 +62,7 @@ VIR_ENUM_IMPL(virStorageFileFormat,
               "cloop", "dmg", "iso",
               "vpc", "vdi",
               /* Not direct file formats, but used for various drivers */
-              "fat", "vhd",
+              "fat", "vhd", "ploop",
               /* Formats with backing file below here */
               "cow", "qcow", "qcow2", "qed", "vmdk")
 
@@ -230,6 +230,8 @@ static struct FileTypeInfo const fileTypeInfo[] = {
                                -1, {0}, 0, 0, 0, 0, NULL, NULL },
     [VIR_STORAGE_FILE_VHD] = { 0, NULL, NULL, LV_LITTLE_ENDIAN,
                                -1, {0}, 0, 0, 0, 0, NULL, NULL },
+    [VIR_STORAGE_FILE_PLOOP] = { 0, NULL, NULL, LV_LITTLE_ENDIAN,
+                               -1, {0}, 0, 0, 0, 0, NULL, NULL },
 
     /* All formats with a backing store probe below here */
     [VIR_STORAGE_FILE_COW] = {

src/util/virstoragefile.h

@@ -72,6 +72,7 @@ typedef enum {
     /* Not direct file formats, but used for various drivers */
     VIR_STORAGE_FILE_FAT,
     VIR_STORAGE_FILE_VHD,
+    VIR_STORAGE_FILE_PLOOP,
 
     /* Not a format, but a marker: all formats below this point have
      * libvirt support for following a backing chain */