Tunable directory for zfs runtime scripts

zpool and zed place scripts in subdirectories of libexecdir. Some
distributions locate architecture independent scripts in other locations
(e.g. Debian). To avoid these paths getting out of sync, centralize the
definitions.

Build zfs-test's default.cfg by Makefile.  Use the new directory
logic building tests/zfs-tests/include/default.cfg.in.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Antonio Russo <antonio.e.russo@gmail.com>
Closes #7597

man/man8/Makefile.am

@@ -19,7 +19,7 @@ EXTRA_DIST = \
 	zfs-mount-generator.8.in
 
 $(nodist_man_MANS): %: %.in
-	-$(SED) -e 's,@libexecdir\@,$(libexecdir),g' \
+	-$(SED) -e 's,@zfsexecdir\@,$(zfsexecdir),g' \
 		-e 's,@runstatedir\@,$(runstatedir),g' \
 		-e 's,@sysconfdir\@,$(sysconfdir),g' \
 		$< >'$@'

man/man8/zed.8.in

@@ -201,7 +201,7 @@ The default directory for enabled ZEDLETs.
 .I @sysconfdir@/zfs/zed.d/zed.rc
 The default rc file for common variables used by ZEDLETs.
 .TP
-.I @libexecdir@/zfs/zed.d
+.I @zfsexecdir@/zed.d
 The default directory for installed ZEDLETs.
 .TP
 .I @runstatedir@/zed.pid

man/man8/zfs-mount-generator.8.in

@@ -56,7 +56,7 @@ touch
 Then, enable the tracking ZEDLET:
 .PP
 .RS 4
-ln -s "@libexecdir@/zfs/zed.d/history_event-zfs-list-cacher.sh" "@sysconfdir@/zfs/zed.d/"
+ln -s "@zfsexecdir@/zed.d/history_event-zfs-list-cacher.sh" "@sysconfdir@/zfs/zed.d"
 
 systemctl enable zed.service