Fix requirements for six package for analytics

[Andrey Sledzinskiy]

We should fix https://github.com/stackforge/fuel-stats/blob/master/analytics/requirements.txt by adding
six>=1.8.0
cause now it's failing when you run - manage_analytics.py --mode test runserver

Traceback (most recent call last):
  File "manage_analytics.py", line 19, in <module>
    from fuel_analytics.api import log
  File "/home/asledzinskiy/Work/fuel-stats/analytics/fuel_analytics/api/log.py", line 20, in <module>
    from fuel_analytics.api.app import app
  File "/home/asledzinskiy/Work/fuel-stats/analytics/fuel_analytics/api/app.py", line 27, in <module>
    from fuel_analytics.api.resources.csv_exporter import bp as csv_exporter_bp
  File "/home/asledzinskiy/Work/fuel-stats/analytics/fuel_analytics/api/resources/csv_exporter.py", line 35, in <module>
    from fuel_analytics.api.resources.utils.stats_to_csv import StatsToCsv
  File "/home/asledzinskiy/Work/fuel-stats/analytics/fuel_analytics/api/resources/utils/stats_to_csv.py", line 18, in <module>
    from six.moves import range
ImportError: cannot import name range

[Alexander Kislitsky (akislitsky)]

Six missed in requirements.txt of analitycs.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/204038

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/204038
Committed: https://git.openstack.org/cgit/stackforge/fuel-stats/commit/?id=3a30fed6791e079a032fdc90f3a8b40a4ab4bde4
Submitter: Jenkins
Branch: master

commit 3a30fed6791e079a032fdc90f3a8b40a4ab4bde4
Author: Alexander Kislitsky <email address hidden>
Date: Tue Jul 21 14:32:18 2015 +0300

    Missed requrement on six package added

    Change-Id: I7b7d55f29b9b016d0f3f680b86e5bf95ae36d526
    Closes-Bug: #1476586

[Nastya Urlapova (aurlapova)]

https://github.com/openstack/fuel-stats/blob/master/analytics/requirements.txt#L6