Support testcrypto.sh usage without including conf.sh

The only variable really needed for the script to work is the path to
the $KEYGEN binary. Allow setting this via an environment variable to
avoid loading conf.sh (and causing a chicken-egg problem). Also make
testcrypto.sh executable to allow its use from conf.sh.

(cherry picked from commit bb1c6bbdc7)

bin/tests/system/testcrypto.sh

@@ -11,14 +11,16 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
-. ../conf.sh
+if test -z "$KEYGEN"; then
+    . ../conf.sh
+    alg="-a $DEFAULT_ALGORITHM -b $DEFAULT_BITS"
+else
+    alg=""
+fi
 
 prog=$0
-
 args=""
-alg="-a $DEFAULT_ALGORITHM -b $DEFAULT_BITS"
 quiet=0
-
 msg="cryptography"
 while test "$#" -gt 0; do
     case $1 in
@@ -62,6 +64,11 @@ while test "$#" -gt 0; do
     shift
 done
 
+if test -z "$alg"; then
+    echo "${prog}: no algorithm selected"
+    exit 1
+fi
+
 if $KEYGEN $args $alg foo > /dev/null 2>&1
 then
     rm -f Kfoo*