iotests: Use configured python

Currently, QEMU's iotests rely on /usr/bin/env to start the correct
Python (that is, at least Python 2.4, but not 3). On systems where
Python 3 is the default, the user has no clean way of making the iotests
use the correct binary.

This commit makes the iotests use the Python selected by configure.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/qemu-iotests/check

@@ -34,6 +34,13 @@ timestamp=${TIMESTAMP:=false}
 # generic initialization
 iam=check
 
+# we need common.env
+if ! . ./common.env
+then
+    echo "$iam: failed to source common.env"
+    exit 1
+fi
+
 # we need common.config
 if ! . ./common.config
 then
@@ -215,9 +222,16 @@ do
 
         start=`_wallclock`
         $timestamp && echo -n "        ["`date "+%T"`"]"
-        [ ! -x $seq ] && chmod u+x $seq # ensure we can run it
+
+        if [ "$(head -n 1 $seq)" == "#!/usr/bin/env python" ]; then
+            run_command="$PYTHON $seq"
+        else
+            [ ! -x $seq ] && chmod u+x $seq # ensure we can run it
+            run_command="./$seq"
+        fi
+
         MALLOC_PERTURB_=${MALLOC_PERTURB_:-$(($RANDOM % 255 + 1))} \
-                ./$seq >$tmp.out 2>&1
+                $run_command >$tmp.out 2>&1
         sts=$?
         $timestamp && _timestamp
         stop=`_wallclock`