Change "-var x=y" to "-var" "x=y"

Author: Ashley Chaloner

packer.py

@@ -182,7 +182,8 @@ def _append_base_arguments(self):
         elif self.only:
             self._add_opt('-only={0}'.format(self._join_comma(self.only)))
         for var, value in self.vars.items():
-            self._add_opt("-var '{0}={1}'".format(var, value))
+            self._add_opt("-var")
+            self._add_opt("{0}={1}".format(var, value))
         if self.var_file:
             self._add_opt('-var-file={0}'.format(self.var_file))