Fixed #20785 -- Corrected exception caught for Oracle LIKE operator detection

The code that tests to see which LIKE expressions to use now runs
using non-error-wrapped cursor, so cx_Oracle exceptions need to be caught
rather than Django DatabaseErrors.

Thanks Trac user ludo for report and initial patch.

django/db/backends/oracle/base.py

@@ -578,7 +578,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
                 cursor.execute("SELECT 1 FROM DUAL WHERE DUMMY %s"
                                % self._standard_operators['contains'],
                                ['X'])
-            except utils.DatabaseError:
+            except DatabaseError: 
                 self.operators = self._likec_operators
             else:
                 self.operators = self._standard_operators