Fix kernel limitation (https://github.com/pypa/virtualenv/issues/596)

Change-Id: I50d729da3eb7a059ce95c7e5839164281210d17c
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index 3d1f1a1..8fe8deb 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -151,7 +151,7 @@
 
 salt_run() {
     [ -e ${VENV_DIR}/bin/activate ] && source ${VENV_DIR}/bin/activate
-    salt-call ${SALT_OPTS} $*
+    python $(which salt-call) ${SALT_OPTS} $*
 }
 
 prepare() {