Fix "pkcs11" system test

- Define the SLOT environment variable before starting the test.  This
    variable defaults to 0 and that does not work with SoftHSM 2.

  - The system test expects the PIN environment variable to be set to
    "1234" while bin/tests/prepare-softhsm2.sh sets it to "0000".
    Update bin/tests/prepare-softhsm2.sh so that it sets the PIN to
    "1234".

  - Move contents of bin/tests/system/pkcs11/prereq.sh to
    bin/tests/system/pkcs11/setup.sh as the former was creating a file
    called "supported" that was getting removed by the latter before
    bin/tests/system/pkcs11/tests.sh could access it.

  - Fix typo in "have_ecx".

bin/tests/prepare-softhsm2.sh

@@ -15,6 +15,6 @@ if [ -n "${SOFTHSM2_CONF}" ] && command -v softhsm2-util >/dev/null; then
     echo "directories.tokendir = ${SOFTHSM2_DIR}/tokens" > "${SOFTHSM2_CONF}"
     echo "objectstore.backend = file" >> "${SOFTHSM2_CONF}"
     echo "log.level = DEBUG" >> "${SOFTHSM2_CONF}"
-    softhsm2-util --init-token --free --pin 0000 --so-pin 0000 --label "softhsm2";
+    softhsm2-util --init-token --free --pin 1234 --so-pin 1234 --label "softhsm2" | awk '/^The token has been initialized and is reassigned to slot/ { print $NF }'
 fi
 exit 0