utilities: a top like tool for ovs-dpctl dump-flows.

utilities: a top like tool for ovs-dpctl dump-flows.

This python script summarizes ovs-dpctl dump-flows content by aggregating
the number of packets, total bytes and occurrence of the following fields:
  - Datapath in_port
  - Ethernet type
  - Source and destination MAC addresses
  - IP protocol
  - Source and destination IPv4 addresses
  - Source and destination IPv6 addresses
  - UDP and TCP destination port
  - Tunnel source and destination addresses

Testing included confirming both mega-flows and non-megaflows are
properly parsed. Bit masks are applied in the case of mega-flows
prior to aggregation.  Test --script parameter which runs in
non-interactive mode. Tested syntax against python 2.4.3, 2.6 and 2.7.
Confirmed script passes pep8 and pylint run as:

pylint --disable=I0011 --include-id=y --reports=n

This tool has been added to these distribution:
  - add ovs-dpctl-top to debian distribution
  - add ovs-dpctl-top to rpm distribution.
  - add ovs-dpctl-top to XenServer RPM.

Signed-off-by: Mark Hamilton <mhamilton@nicira.com>
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>