RE-escape the prompt string returned from the switch

If we don't, unexpected RE metacharacters could cause all kinds of
trouble.

Change-Id: I34c8bdec99493cb018197f873397d370a831f09f
diff --git a/drivers/CiscoSX300.py b/drivers/CiscoSX300.py
index 2060c31..c00021c 100644
--- a/drivers/CiscoSX300.py
+++ b/drivers/CiscoSX300.py
@@ -443,7 +443,7 @@
                 logging.error("Login failure: %s\n", self.connection.match)
                 raise IOError
             elif index == 2:
-                self._prompt_name = self.connection.match.group(1).strip()
+                self._prompt_name = re.escape(self.connection.match.group(1).strip())
                 # Horrible output from the switch at login time may
                 # confuse our pexpect stuff here. If we've somehow got
                 # multiple lines of output, clean up and just take the