pkg_resources.DistributionNotFound: The 'tenacity>=4.6.0' distribution was not found and is required by gnocchi

I am trying to install tacker via devstack as mentioned here - https://docs.openstack.org/tacker/latest/install/devstack.html. I did everything as mentioned but the installation fails with this error - "2018-07-09 18:35:18.635 | pkg_resources.DistributionNotFound: The 'tenacity>=4.6.0' distribution was not found and is required by gnocchi"

Can you please check? I used the branch stable/pike to clone devstack.

2018-07-09 18:35:18.214 | ++/opt/stack/ceilometer/devstack/plugin.sh:configure_gnocchi:185 sudo mkdir -p /var/cache/gnocchi
2018-07-09 18:35:18.223 | ++/opt/stack/ceilometer/devstack/plugin.sh:configure_gnocchi:186 sudo chown stack /var/cache/gnocchi
2018-07-09 18:35:18.232 | ++/opt/stack/ceilometer/devstack/plugin.sh:configure_gnocchi:187 rm -f '/var/cache/gnocchi/*'
2018-07-09 18:35:18.238 | ++/opt/stack/ceilometer/devstack/plugin.sh:configure_gnocchi:189 gnocchi-upgrade
2018-07-09 18:35:18.634 | Traceback (most recent call last):
2018-07-09 18:35:18.634 | File "/usr/local/bin/gnocchi-upgrade", line 6, in <module>
2018-07-09 18:35:18.634 | from pkg_resources import load_entry_point
2018-07-09 18:35:18.634 | File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3098, in <module>
2018-07-09 18:35:18.634 | @_call_aside
2018-07-09 18:35:18.634 | File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3082, in _call_aside
2018-07-09 18:35:18.634 | f(*args, **kwargs)
2018-07-09 18:35:18.634 | File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 3111, in _initialize_master_working_set
2018-07-09 18:35:18.635 | working_set = WorkingSet._build_master()
2018-07-09 18:35:18.635 | File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 575, in _build_master
2018-07-09 18:35:18.635 | return cls._build_from_requirements(__requires__)
2018-07-09 18:35:18.635 | File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 588, in _build_from_requirements
2018-07-09 18:35:18.635 | dists = ws.resolve(reqs, Environment())
2018-07-09 18:35:18.635 | File "/usr/local/lib/python2.7/dist-packages/pkg_resources/__init__.py", line 777, in resolve
2018-07-09 18:35:18.635 | raise DistributionNotFound(req, requirers)
2018-07-09 18:35:18.635 | pkg_resources.DistributionNotFound: The 'tenacity>=4.6.0' distribution was not found and is required by gnocchi
2018-07-09 18:35:18.652 | +/opt/stack/ceilometer/devstack/plugin.sh:configure_gnocchi:1 exit_trap
2018-07-09 18:35:18.656 | +./stack.sh:exit_trap:521 local r=1
2018-07-09 18:35:18.661 | ++./stack.sh:exit_trap:522 jobs -p
2018-07-09 18:35:18.665 | +./stack.sh:exit_trap:522 jobs=
2018-07-09 18:35:18.670 | +./stack.sh:exit_trap:525 [[ -n '' ]]
2018-07-09 18:35:18.674 | +./stack.sh:exit_trap:531 '[' -f /tmp/tmp.pji74xOwsQ ']'
2018-07-09 18:35:18.678 | +./stack.sh:exit_trap:532 rm /tmp/tmp.pji74xOwsQ
2018-07-09 18:35:18.683 | +./stack.sh:exit_trap:536 kill_spinner
2018-07-09 18:35:18.688 | +./stack.sh:kill_spinner:417 '[' '!' -z '' ']'
2018-07-09 18:35:18.692 | +./stack.sh:exit_trap:538 [[ 1 -ne 0 ]]
2018-07-09 18:35:18.696 | +./stack.sh:exit_trap:539 echo 'Error on exit'
2018-07-09 18:35:18.696 | Error on exit
2018-07-09 18:35:18.701 | +./stack.sh:exit_trap:541 type -p generate-subunit
2018-07-09 18:35:18.705 | +./stack.sh:exit_trap:542 generate-subunit 1531159878 1440 fail
2018-07-09 18:35:19.059 | +./stack.sh:exit_trap:544 [[ -z /opt/stack/logs ]]
2018-07-09 18:35:19.064 | +./stack.sh:exit_trap:547 /opt/stack/devstack/tools/worlddump.py -d /opt/stack/logs
2018-07-09 18:35:19.494 | +./stack.sh:exit_trap:556 exit 1