Skip bad versions of iso8601

0.1.7 is now released (https://pypi.python.org/pypi/iso8601). We
do need to allow folks to use the old 0.1.4 or the new  0.1.7 and
avoid the two bad versions (0.1.5 and 0.1.6)

Closes-Bug: 1241460

Change-Id: I96bfd8f27d9f7327c4c353c5f57660aabaa8c735

requirements.txt

@@ -6,7 +6,7 @@ greenlet>=0.3.2
 requests>=1.1
 Routes>=1.12.3
 prettytable>=0.6,<0.8
-iso8601>=0.1.4
+iso8601>=0.1.4,!=0.1.5,!=0.1.6
 anyjson>=0.3.3
 kombu>=2.4.8
 argparse