Add showOvsdbMdsal.py tool

Add showOvsdbMdsal.py tool

This tool can provide useful info in regards to ovsdb's mdsal structures.
It looks at the operational or config trees in mdsal, depending on the
parameter '--config':

Patch set 2: code review

$ ./showOvsdbMdsal.py -h
Usage: showOvsdbMdsal.py [options]

Options:
  --version             show program's version number and exit
  -h, --help            show this help message and exit
  -d, --debug           Verbosity. Can be provided multiple times for more
                        debug.
  -n, --noalias         Do not map nodeId of bridges to an alias
  -i ODLIP, --ip=ODLIP  opendaylights ip address
  -t ODLPORT, --port=ODLPORT
                        opendaylights listening tcp port on restconf
                        northbound
  -u ODLUSERNAME, --user=ODLUSERNAME
                        opendaylight restconf username
  -p ODLPASSWORD, --password=ODLPASSWORD
                        opendaylight restconf password
  -c, --config          parse mdsal restconf config tree instead of
                        operational tree
  -f, --hide-flows      hide flows

Examples of what to expect:

  https://gist.githubusercontent.com/anonymous/3a952cec49ef92461752/raw/7abfedcd7790acc5b5cef07a2c08da0405f303c6/gistify465337.txt

Change-Id: Ica94e00a14d17682acdedad3b495833de330afc4
Signed-off-by: Flavio Fernandes <ffernand@redhat.com>