Hey, I get this error everytime I try to run ./stack on any branch:

Obtaining file:///opt/stack/glance
 Exception:
 Traceback (most recent call last):
 File "/usr/local/lib/python2.7/dist-packages/pip/basecommand.py", line 215, in main
 status = self.run(options, args)
 File "/usr/local/lib/python2.7/dist-packages/pip/commands/install.py", line 335, in run
 wb.build(autobuilding=True)
 File "/usr/local/lib/python2.7/dist-packages/pip/wheel.py", line 749, in build
 self.requirement_set.prepare_files(self.finder)
 File "/usr/local/lib/python2.7/dist-packages/pip/req/req_set.py", line 380, in prepare_files
 ignore_dependencies=self.ignore_dependencies))
 File "/usr/local/lib/python2.7/dist-packages/pip/req/req_set.py", line 521, in _prepare_file
 req_to_install.check_if_exists()
 File "/usr/local/lib/python2.7/dist-packages/pip/req/req_install.py", line 1036, in check_if_exists
 self.req.name
 File "/usr/local/lib/python2.7/dist-packages/pip/_vendor/pkg_resources/__init__.py", line 558, in get_distribution
 dist = get_provider(dist)
 File "/usr/local/lib/python2.7/dist-packages/pip/_vendor/pkg_resources/__init__.py", line 432, in get_provider
 return working_set.find(moduleOrReq) or require(str(moduleOrReq))[0]
 File "/usr/local/lib/python2.7/dist-packages/pip/_vendor/pkg_resources/__init__.py", line 968, in require
 needed = self.resolve(parse_requirements(requirements))
 File "/usr/local/lib/python2.7/dist-packages/pip/_vendor/pkg_resources/__init__.py", line 859, in resolve
 raise VersionConflict(dist, req).with_context(dependent_req)
 ContextualVersionConflict: (keystoneauth1 2.4.3 (/usr/local/lib/python2.7/dist-packages), 
 Requirement.parse('keystoneauth1>=2.16.0'), set(['castellan']))
 +inc/python:pip_install:1                  exit_trap
 +./stack.sh:exit_trap:491                  local r=2
 ++./stack.sh:exit_trap:492                  jobs -p
 +./stack.sh:exit_trap:492                  jobs=
 +./stack.sh:exit_trap:495                  [[ -n '' ]]
 +./stack.sh:exit_trap:501                  kill_spinner
 +./stack.sh:kill_spinner:387               '[' '!' -z '' ']'
 +./stack.sh:exit_trap:503                  [[ 2 -ne 0 ]]
 +./stack.sh:exit_trap:504                  echo 'Error on exit'
 Error on exit
 +./stack.sh:exit_trap:505                  generate-subunit 1499173157 64 fail
 +./stack.sh:exit_trap:506                  [[ -z /opt/stack/logs ]]
 +./stack.sh:exit_trap:509                  /opt/stack/devstack/tools/worlddump.py -d /opt/stack/logs
 World dumping... see /opt/stack/logs/worlddump-2017-07-04-130022.txt for details
 +./stack.sh:exit_trap:515                  exit 2