updated README file to include persistence framework setup instructions

updated README file to include persistence framework setup instructions
updated db api.py unset_attachment method to return port
moved db_conn.ini into cisco/conf/ with other configuration files
updated l2network_plugin_configuration.py to get db config
cleaned up l2network_db.py - removed config parser code as using cisco config parser
updated l2network_db.py to raise specific exceptions in error cases
updated create_vlanid method in l2network_db.py to not raise exception if vlan rows exist
updated portprofile and portprofile_binding methods to include tenant_id as an argument
added cisco/db/test_database.py containing unit tests for quantum and l2network_plugin tables
edited get_pp_binding method in l2network_db.py to return empty list when no results found
pep8 checks done