Sync iso8601 requirement and fixes test case failures

1. Sync requirements from global Iece0116d3c412216251e2d7fbffe10bfe2c1c789
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>
(cherry picked from commit 8160ae293383ec600c05fd2e4b38164bca7704c4)
Conflicts:
	glance/tests/unit/v1/test_registry_api.py
	requirements.txt