Pin more-itertools==5.0.0

Pin more-itertools==5.0.0

Newer networking-l2gw is pulling in newer versions of
more-itertools which fails with our python2 env. This
will get around that until we can get up to speed with
python3.

the error seen in the console log is:

01:20:28 ERROR: Package 'more-itertools' requires a different Python: 2.7.5 not in '>=3.4'
01:20:28
Build step 'Execute shell' marked build as failure

example job:
https://jenkins.opendaylight.org/releng/view/netvirt/job/netvirt-csit-hwvtep-1node-0cmb-1ctl-2cmp-openstack-queens-upstream-stateful-sodium/105/consoleFull

Signed-off-by: Jamo Luhrsen <jluhrsen@gmail.com>
Change-Id: I3e9a73f490c084b035f71af37e39315b068f8306