add required python modules(six,iso8601,fixtures) to requirements.txt
These modules of six, iso8601, fixtures, are requiementd by following tempest modules.
But they are missing in requirements.txt.
./tempest/openstack/common/log.py:42:from six import moves
./tempest/openstack/common/timeutils.py:25:import iso8601
./tempest/api/compute/admin/test_aggregates.py:18:import fixtures
./tempest/test.py:22:import fixtures
Closes-Bug: #1225723
Change-Id: I5a43559630714c504dba4ef79ba9ee29128dfc69
diff --git a/requirements.txt b/requirements.txt
index ab48ec5..b15fb92 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -19,3 +19,6 @@
testrepository>=0.0.17
oslo.config>=1.1.0
eventlet>=0.13.0
+six<1.4.0
+iso8601>=0.1.4
+fixtures>=0.3.14