Disable ConfigParser interpolation (lp#1025993)

Change-Id: Iefc0e92e31a8e6fcf614c4719a6551c01cbdd6ec
diff --git a/tempest/config.py b/tempest/config.py
index ce79044..4906c4c 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -33,7 +33,7 @@
 
     def get(self, item_name, default_value=None):
         try:
-            return self.conf.get(self.SECTION_NAME, item_name)
+            return self.conf.get(self.SECTION_NAME, item_name, raw=True)
         except (ConfigParser.NoSectionError, ConfigParser.NoOptionError):
             return default_value