hvm: Allow blktap to be able to be booted as system volume for PV-on-HVM

When blktap was booting system volume, PV-on-HVM domain was not able
to be  started.

The configuration file is specified as follows.
disk = [ 'tap:aio:/xen/test/rhel5ga_full.img,hda,w' ]

The error occurred by the initialization of system volume in qemu-dm.
qemu: could not open hard disk image 'aio:/xen/test/rhel5ga_full.img'

Signed-off-by: Takanori Kasai <kasai.takanori@jp.fujitsu.com>
Signed-off-by: Tomonari Horikoshi <t.horikoshi@jp.fujitsu.com>
Signed-off-by: Tsunehisa Doi <Doi.Tsunehisa@jp.fujitsu.com>
Signed-off-by: Keir Fraser <keir@xensource.com>

tools/ioemu/xenstore.c

@@ -173,10 +173,12 @@ void xenstore_parse_domain_config(int domid)
         }
         /* open device now if media present */
         if (params[0]) {
+            char *p = strchr(params, ':');
+            p = p ? p+1 : params; /* skip colon separator if present */
             if (bdrv_open(bs_table[hd_index + (is_scsi ? MAX_DISKS : 0)],
-                          params, 0 /* snapshot */) < 0)
+                          p, 0 /* snapshot */) < 0)
                 fprintf(stderr, "qemu: could not open hard disk image '%s'\n",
-                        params);
+                        p);
         }
     }