Normalize_time() always return naive object

Currently the timeutils.normalize_time() returns naive datetime
object when parameter timestamp is an naive object or a non-UTC
aware datetime object, and returns aware datetime object if
parameter timestamp is a UTC aware datetime object.

The basic problem here is that utcoffset() of None means the object is naive
but a utcoffset() of zero means that the object is aware but represents
UTC time.

This is fragile implementation and will trigger potential issue, because
aware/native datetime is not interoperatable. For example,
"timeutils.utcnow() > timeutils.normalize_time(m)" will success at most
time, while trigger TypeError if m is a UTC aware object.

We want to normalize all objects into naive objects.

Fixes bug 1048636

Change-Id: I4a09246fa8f0dd63ca54362b877aa825d9b79772
Signed-off-by: Yunhong, Jiang <yunhong.jiang@intel.com>
(cherry picked from commit b81938dc2fec8f6e15b0b3dcb8eabc276e647af4)