tests/sys/opencrypto/runtests: apply minor polish to test script

- Refactor kld loading/unloading logic:
-- Use a loop instead of an unrolled one.
-- Check for the module being loaded before trying to load it, to reduce
   noise when loading modules that are already loaded.
-- Don't mute stderr from kldload -- it could be potentially useful to
   the tester.
-- In the event that the test script was terminated early, it would leave
   the modules still attached to the system (which is undesirable).
   Always unload the modules at test end with EXIT/SIGINT/SIGTERM so the
   system is returned to its former operating state as best possible.
   Unload the modules in reverse order, in part for consistency and/or
   dependency reasons.

MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon

tests/sys/opencrypto/runtests.sh

@@ -29,20 +29,33 @@
 # $FreeBSD$
 #
 
-set -e
+set -ex
 
 if [ ! -d /usr/local/share/nist-kat ]; then
 	echo 'Skipping, nist-kat package not installed for test vectors.'
 	exit 0
 fi
 
-if kldload aesni 2>/dev/null; then
-	unloadaesni=1
-fi
+loaded_modules=
+cleanup_tests()
+{
+	trap - EXIT INT TERM
 
-if kldload cryptodev 2>/dev/null; then
-	unloadcdev=1
-fi
+	set +e
+
+	# Unload modules in reverse order
+	for loaded_module in $(echo $loaded_modules | tr ' ' '\n' | sort -r); do
+		kldunload $loaded_module
+	done
+}
+trap cleanup_tests EXIT INT TERM
+
+for required_module in aesni cryptodev; do
+	if ! kldstat -q -m $required_module; then
+		kldload $required_module
+		loaded_modules="$loaded_modules $required_module"
+	fi
+done
 
 # Run software crypto test
 oldcdas=$(sysctl -e kern.cryptodevallowsoft)
@@ -51,10 +64,3 @@ sysctl kern.cryptodevallowsoft=1
 python $(dirname $0)/cryptotest.py
 
 sysctl "$oldcdas"
-
-if [ x"$unloadcdev" = x"1" ]; then
-	kldunload cryptodev
-fi
-if [ x"$unloadaesni" = x"1" ]; then
-	kldunload aesni
-fi