Cleanup contrib/initramfs automake

The initramfs hook scripts depend on Makefile.  This way, if the
substitution code is changed, they should update.  This brings it in
line with etc/init.d (which was modified to match the example in the
automake docs).

The initramfs hook script cleaning now matches etc/init.d.

There was a mix of SUBDIRS recursion and custom install rules for files
in subdirectories.  This was duplicated for the "hooks" and "scripts"
subdirectories.  Now everything uses SUBDIRS.

I fixed the substitution of DEFAULT_INITCONF_DIR for hooks/zfs.

Reviewed-By: Andrey Prokopenko <job@terem.fr>
Reviewed-By: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-By: Tom Caputi <tcaputi@datto.com>
Signed-off-by: Richard Laager <rlaager@wiktel.com>
Closes #10027

contrib/initramfs/hooks/Makefile.am

@@ -6,18 +6,13 @@ hooks_SCRIPTS = \
 EXTRA_DIST = \
 	$(top_srcdir)/contrib/initramfs/hooks/zfs.in
 
-$(hooks_SCRIPTS):%:%.in
+$(hooks_SCRIPTS):%:%.in Makefile
 	-$(SED) -e 's,@sbindir\@,$(sbindir),g' \
 		-e 's,@sysconfdir\@,$(sysconfdir),g' \
 		-e 's,@udevdir\@,$(udevdir),g' \
 		-e 's,@udevruledir\@,$(udevruledir),g' \
 		-e 's,@mounthelperdir\@,$(mounthelperdir),g' \
+		-e 's,@DEFAULT_INITCONF_DIR\@,$(DEFAULT_INITCONF_DIR),g' \
 		$< >'$@'
 
-# Double-colon rules are allowed; there are multiple independent definitions.
-clean-local::
-	-$(RM) $(hooks_SCRIPTS)
-
-# Double-colon rules are allowed; there are multiple independent definitions.
-distclean-local::
-	-$(RM) $(hooks_SCRIPTS)
+CLEANFILES = $(hooks_SCRIPTS)