tests-1.3: add bsn_flow_checksum testsuite

See the Loxigen extension bsn_flow_checksum. This extension maintains checksums
per table and for a configurable number of buckets in each table. The checksums
are sent to the switch in the cookie field of the flow-add. These checksums are
intended to be used for a hash-tree like synchronization scheme.
bsn_flow_checksum.FlowChecksum: check intermediate checksums

Also fixed a bug where 'i' and the checksum were not correspondent.
Merge into master from pull request #112:
tests-1.3: add bsn_flow_checksum testsuite (https://github.com/floodlight/oftest/pull/112)