configure: Enable out-of-tree iotests

In order to allow out-of-tree iotests, create a symlink for the check
script in the build tree.

While doing so, also write configured options relevant to the iotests to
common.env in the build tree; currently, this is the command to invoke
Python 2.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

configure

@@ -5273,6 +5273,18 @@ if test "$docs" = "yes" ; then
   mkdir -p QMP
 fi
 
+# set up qemu-iotests in this build directory
+iotests_common_env="tests/qemu-iotests/common.env"
+iotests_check="tests/qemu-iotests/check"
+
+echo "# Automatically generated by configure - do not modify" > "$iotests_common_env"
+echo >> "$iotests_common_env"
+echo "export PYTHON='$python'" >> "$iotests_common_env"
+
+if [ ! -e "$iotests_check" ]; then
+    symlink "$source_path/$iotests_check" "$iotests_check"
+fi
+
 # Save the configure command line for later reuse.
 cat <<EOD >config.status
 #!/bin/sh