scripts: remove use of realpath and fix external.test

`external.test` could fail quietly for not finding `ping.test` for
out-of-tree builds. Make it look relative to the script location.

scripts/external.test

@@ -2,6 +2,8 @@
 
 # external.test
 
+SCRIPT_DIR="$(dirname "$0")"
+
 server=www.wolfssl.com
 ca=./certs/wolfssl-website-ca.pem
 
@@ -32,7 +34,7 @@ if [ $? -ne 0 ]; then
     fi
 
     # is our desired server there?
-    ./scripts/ping.test $server 2
+    ${SCRIPT_DIR}/ping.test $server 2
     RESULT=$?
     [ $RESULT -ne 0 ] && exit 0
 

scripts/openssl.test

@@ -2,7 +2,8 @@
 
 #openssl.test
 
-CERT_DIR="$(realpath $(dirname $0)/../certs)"
+CERT_DIR="$PWD/$(dirname "$0")/../certs"
+
 if ! test -n "$WOLFSSL_OPENSSL_TEST"; then
     echo "WOLFSSL_OPENSSL_TEST NOT set, won't run"
     exit 0