Issue warning when deprecated drive parameter boot=on|off is used

Releases of qemu-kvm will be interrupted at qemu 1.3.0.
Users should switch to plain qemu releases.
To avoid breaking scenarios which are setup with command line
options specific to qemu-kvm, port these switches from qemu-kvm
to qemu.git.

Port drive boot option. From the qemu-kvm original commit message:

We do not want to maintain this option forever. It will be removed after
a grace period of a few releases. So warn the user that this option has
no effect and will become invalid soon.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

blockdev.c

@@ -433,6 +433,12 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
         return NULL;
     }
 
+    if (qemu_opt_get(opts, "boot") != NULL) {
+        fprintf(stderr, "qemu-kvm: boot=on|off is deprecated and will be "
+                "ignored. Future versions will reject this parameter. Please "
+                "update your scripts.\n");
+    }
+
     on_write_error = BLOCKDEV_ON_ERROR_ENOSPC;
     if ((buf = qemu_opt_get(opts, "werror")) != NULL) {
         if (type != IF_IDE && type != IF_SCSI && type != IF_VIRTIO && type != IF_NONE) {

qemu-config.c

@@ -114,6 +114,10 @@ static QemuOptsList qemu_drive_opts = {
             .name = "copy-on-read",
             .type = QEMU_OPT_BOOL,
             .help = "copy read data from backing file into image file",
+        },{
+            .name = "boot",
+            .type = QEMU_OPT_BOOL,
+            .help = "(deprecated, ignored)",
         },
         { /* end of list */ }
     },