Canonicalize python shebangs

Prefer Python 3 by default to satisfy rpm build.

Detect if the sed we are using supports --in-place or prefers -i '' at
configure time.

Signed-off-by: Ryan Moeller <ryan@ixsystems.com>

cmd/arc_summary/arc_summary2

@@ -1,4 +1,4 @@
-#!/usr/bin/python2
+#!/usr/bin/env python2
 #
 # $Id: arc_summary.pl,v 388:e27800740aa2 2011-07-08 02:53:29Z jhell $
 #

cmd/arc_summary/arc_summary3

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 #
 # Copyright (c) 2008 Ben Rockwood <benr@cuddletech.com>,
 # Copyright (c) 2010 Martin Matuska <mm@FreeBSD.org>,

cmd/arcstat/Makefile.am

@@ -8,6 +8,6 @@ dist_bin_SCRIPTS = arcstat
 #
 if USING_PYTHON_2
 install-exec-hook:
-	sed --in-place 's|^#!/usr/bin/python3|#!/usr/bin/python2|' \
+	sed ${ac_inplace} -e 's|^#!/usr/bin/env python3|#!/usr/bin/env python2|' \
 	    $(DESTDIR)$(bindir)/arcstat
 endif

cmd/arcstat/arcstat

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 #
 # Print out ZFS ARC Statistics exported via kstat(1)
 # For a definition of fields, or usage, use arctstat.pl -v

cmd/dbufstat/Makefile.am

@@ -8,6 +8,6 @@ dist_bin_SCRIPTS = dbufstat
 #
 if USING_PYTHON_2
 install-exec-hook:
-	sed --in-place 's|^#!/usr/bin/python3|#!/usr/bin/python2|' \
+	sed ${ac_inplace} -e 's|^#!/usr/bin/env python3|#!/usr/bin/env python2|' \
 	    $(DESTDIR)$(bindir)/dbufstat
 endif

cmd/dbufstat/dbufstat

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 #
 # Print out statistics for all cached dmu buffers.  This information
 # is available through the dbufs kstat and may be post-processed as

config/always-sed.m4

@@ -0,0 +1,16 @@
+dnl #
+dnl # Set the flags used for sed in-place edits.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_SED], [
+	ac_inplace=""
+	AC_CACHE_CHECK([for sed --in-place], [ac_cv_path_SED],
+		[AC_PATH_PROGS_FEATURE_CHECK([SED], [sed],
+			[[tmpfile=$(mktemp)
+			  echo foo > $tmpfile
+			  $ac_path_SED --in-place 's#foo#bar#' $tmpfile \
+			  && ac_cv_path_SED=$ac_path_SED
+			  rm $tmpfile]],
+			[ac_inplace="-i ''"])])
+	AS_IF([test "x$ac_inplace" = "x"], [ac_inplace="--in-place"])
+	AC_SUBST([ac_inplace])
+])

config/zfs-build.m4

@@ -165,6 +165,7 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS], [
 	ZFS_AC_CONFIG_ALWAYS_ARCH
 	ZFS_AC_CONFIG_ALWAYS_PYTHON
 	ZFS_AC_CONFIG_ALWAYS_PYZFS
+	ZFS_AC_CONFIG_ALWAYS_SED
 ])
 
 AC_DEFUN([ZFS_AC_CONFIG], [

tests/test-runner/bin/Makefile.am

@@ -9,7 +9,7 @@ dist_pkgdata_SCRIPTS = \
 #
 if USING_PYTHON_2
 install-data-hook:
-	sed --in-place 's|^#!/usr/bin/python3|#!/usr/bin/python2|' \
+	sed ${ac_inplace} -e 's|^#!/usr/bin/env python3|#!/usr/bin/env python2|' \
 	    $(DESTDIR)$(pkgdatadir)/test-runner.py \
 	    $(DESTDIR)$(pkgdatadir)/zts-report.py
 endif

tests/test-runner/bin/test-runner.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 #
 # This file and its contents are supplied under the terms of the

tests/test-runner/bin/zts-report.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 #
 # This file and its contents are supplied under the terms of the