Leverage on PBR

Leverage on PBR

It fixes requirements and constraints by switching to PBR [1].
It synchronizes requirements with OpenStack stable/stein and then
adds constraints to pip calls.

It also updates flask-restful-swagger to conform with OpenStack
upper-constraints [2] and the pip API calls.

It updates the unit tests verifying a few package versions.

It stops checking unicodecsv in py3 env which is against the
requirements defined in OpenStack.

It also skips one test indirectly highlighting that the pip usage
is incorrect [3]

[1] http://testresults.opnfv.org/functest/dockerslicing/
[2] https://github.com/rantav/flask-restful-swagger/commit/fd418b50723fe1e79f495aa400a8e9f055a5be27
[3] https://github.com/pypa/pip/issues/3889

Change-Id: I635bdb9d7411e619cee911b633fa8ad591a393a0
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>