classes: Fix alternatives and rc.d ordering

When using an alternative as an initscript, the ordering between
update-rc.d and update-alternatives tasks during prerm and postinst
tasks must always be the following in order to work:
  * prerm:
    - stop daemon
    - remove alternative

  * postinst:
    - add alternative
    - start daemon

This patchset adds comments to the scripts generated by both classes and
organize the generated sections based on those comments.

[YOCTO #10433]

Changes since v5:
    - Remove boolean in d.getVar() calls

(From OE-Core rev: aa87b1a4dcc14e4dfe719b6c55045c5662bc59c2)

Signed-off-by: David Vincent <freesilicon@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/update-rc.d.bbclass

@@ -35,6 +35,7 @@ fi
 }
 
 updatercd_postinst() {
+# Begin section update-rc.d
 if ${@use_updatercd(d)} && type update-rc.d >/dev/null 2>/dev/null; then
 	if [ -n "$D" ]; then
 		OPT="-r $D"
@@ -43,12 +44,15 @@ if ${@use_updatercd(d)} && type update-rc.d >/dev/null 2>/dev/null; then
 	fi
 	update-rc.d $OPT ${INITSCRIPT_NAME} ${INITSCRIPT_PARAMS}
 fi
+# End section update-rc.d
 }
 
 updatercd_prerm() {
+# Begin section update-rc.d
 if ${@use_updatercd(d)} && [ -z "$D" -a -x "${INIT_D_DIR}/${INITSCRIPT_NAME}" ]; then
 	${INIT_D_DIR}/${INITSCRIPT_NAME} stop || :
 fi
+# End section update-rc.d
 }
 
 updatercd_postrm() {
@@ -111,13 +115,25 @@ python populate_packages_updatercd () {
         postinst = d.getVar('pkg_postinst_%s' % pkg)
         if not postinst:
             postinst = '#!/bin/sh\n'
-        postinst += localdata.getVar('updatercd_postinst')
+        postinst = postinst.splitlines(True)
+        try:
+            index = postinst.index('# End section update-alternatives\n')
+            postinst.insert(index + 1, localdata.getVar('updatercd_postinst'))
+        except ValueError:
+            postinst.append(localdata.getVar('updatercd_postinst'))
+        postinst = ''.join(postinst)
         d.setVar('pkg_postinst_%s' % pkg, postinst)
 
         prerm = d.getVar('pkg_prerm_%s' % pkg)
         if not prerm:
             prerm = '#!/bin/sh\n'
-        prerm += localdata.getVar('updatercd_prerm')
+        prerm = prerm.splitlines(True)
+        try:
+            index = prerm.index('# Begin section update-alternatives\n')
+            prerm.insert(index, localdata.getVar('updatercd_prerm'))
+        except ValueError:
+            prerm.append(localdata.getVar('updatercd_prerm'))
+        prerm = ''.join(prerm)
         d.setVar('pkg_prerm_%s' % pkg, prerm)
 
         postrm = d.getVar('pkg_postrm_%s' % pkg)