Sync iso8601 requirement and fixes test case failures

1. Sync requirements from global.
2. iso8601>=0.1.7 "parse_date()" could successfully handle date string
which only have date part like YYYY-MM-DD, it caused two Glance test
cases failure.

Fixes bug: 1242501

Change-Id: I2625eb3888111829a9da4d093b34193b8795f264
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>