image creation: allow overriding .rootfs suffix

By default, the image file name contains ".rootfs" to distinguish the
image file from other files created during image building. However,
for certain image types (for example, .hddimg) the ".rootfs" suffix is
redundant because the type suffix alone already uniquely identifies
the main image file (core-image-minimal-intel-corei7-64.hddimg instead
of core-image-minimal-intel-corei7-64.rootfs.hddimg).

With this change, distros that prefer the shorter image name can
override the .rootfs suffix unconditionally with
   IMAGE_NAME_SUFFIX ?= '' in their distro configuration
or with some condition check like this:
   python () {
       if <whole-disk image format active>:
           d.setVar('IMAGE_NAME_SUFFIX', '')
   }

The exact logic when to remove the extra suffix depends on the distro
and how it enables its own image type.

(From OE-Core rev: 380ee36811939d947024bf78de907e3c071b834f)

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/image.bbclass

@@ -387,7 +387,7 @@ python () {
                     subimages.append(realt + "." + ctype)
 
         if realt not in alltypes:
-            cmds.append(localdata.expand("\trm ${IMAGE_NAME}.rootfs.${type}"))
+            cmds.append(localdata.expand("\trm ${IMAGE_NAME}${IMAGE_NAME_SUFFIX}.${type}"))
         else:
             subimages.append(realt)
 
@@ -474,7 +474,7 @@ python create_symlinks() {
     manifest_name = d.getVar('IMAGE_MANIFEST', True)
     taskname = d.getVar("BB_CURRENTTASK", True)
     subimages = (d.getVarFlag("do_" + taskname, 'subimages', False) or "").split()
-    imgsuffix = d.getVarFlag("do_" + taskname, 'imgsuffix', True) or ".rootfs."
+    imgsuffix = d.getVarFlag("do_" + taskname, 'imgsuffix', True) or "${IMAGE_NAME_SUFFIX}."
     os.chdir(deploy_dir)
 
     if not link_name: