avocado.utils: Introduce data_structures module

Introduce a module with useful classes for use inside
avocado core code or plugins. We start with the Borg
class, a design pattern considered to be better than
the Singleton [1]

[1] http://www.aleax.it/5ep.htmlSigned-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

avocado/utils/data_structures.py

+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+#
+# See LICENSE for more details.
+#
+# Copyright: Red Hat Inc. 2014
+#
+# Authors: Ruda Moura <rmoura@redhat.com>
+#          Lucas Meneghel Rodrigues <lmr@redhat.com>
+#
+"""
+This module contains handy classes that can be used inside
+avocado core code or plugins.
+"""
+
+
+class Borg:
+
+    """
+    Multiple instances of this class will share the same state.
+
+    This is considered a better design pattern in Python than
+    more popular patterns, such as the Singleton. Inspired by
+    Alex Martelli's article mentioned below:
+
+    :see: http://www.aleax.it/5ep.html
+    """
+
+    __shared_state = {}
+
+    def __init__(self):
+        self.__dict__ = self.__shared_state