Verify ZFS Test Suite scripts executability

This change adds a make target 'testscheck' which verifies all ksh test
scripts, part of the ZFS Test Suite, have their executable bit set:
this should avoid adding new test scripts that cannot be executed by
the test-runner.py which would result in the following warning message:

   Warning: Test removed from TestGroup because it failed verification.

This also verifies both *.cfg and *.kshlib files used in the ZFS Test
Suite are not executable.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #7131

Makefile.am

@@ -41,7 +41,7 @@ dist-hook:
 	sed -i 's/Release:[[:print:]]*/Release:      $(RELEASE)/' \
 		$(distdir)/META
 
-checkstyle: cstyle shellcheck flake8 commitcheck mancheck
+checkstyle: cstyle shellcheck flake8 commitcheck mancheck testscheck
 
 commitcheck:
 	@if git rev-parse --git-dir > /dev/null 2>&1; then \
@@ -68,6 +68,14 @@ mancheck:
 			xargs mandoc -Tlint -Werror; \
 	fi
 
+testscheck:
+	@find ${top_srcdir}/tests/zfs-tests/tests -type f \
+		\( -name '*.ksh' -not -executable \) -o \
+		\( -name '*.kshlib' -executable \) -o \
+		\( -name '*.cfg' -executable \) | \
+		xargs -r stat -c '%A %n' | \
+		awk '{c++; print} END {if(c>0) exit 1}'
+
 lint: cppcheck paxcheck
 
 cppcheck: