busybox-initrd: auto pv from busybox

Not hardcoding the version of busybox from the core layer in this layer
is a small improvement for maintenance.

But the main motivation is to support the following layer combination
without getting a parse error from bitbake:
- poky LTS, branch = kirkstone
- meta-lts-mixins, branch = kirkstone/go
- meta-lts-mixins, branch = kirkstone/rust
- meta-virtualization, branch = master

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

recipes-core/busybox/busybox-initrd.bb

@@ -1,5 +1,19 @@
 FILESEXTRAPATHS:prepend := "${THISDIR}/busybox-initrd:${COREBASE}/meta/recipes-core/busybox/busybox:${COREBASE}/meta/recipes-core/busybox/files:"
 
+def get_busybox_pv(d):
+    import re
+    corebase = d.getVar('COREBASE')
+    bb_dir = os.path.join(corebase, 'meta', 'recipes-core', 'busybox')
+    if os.path.isdir(bb_dir):
+        re_bb_name = re.compile(r"busybox_([0-9.]*)\.bb")
+        for bb_file in os.listdir(bb_dir):
+            result = re_bb_name.match(bb_file)
+            if result:
+                return result.group(1)
+    bb.fatal("Cannot find busybox recipe in %s" % bb_dir)
+
+PV := "${@get_busybox_pv(d)}"
+
 require recipes-core/busybox/busybox_${PV}.bb
 
 SRC_URI += "file://init.cfg \