oslo_utils.timeutils.isotime() is deprecated as of 1.6 so we need
to stop using it.
The deprecation message says to use datetime.datetime.isoformat()
instead, but the format of the string generated by isoformat isn't
the same as the format of the string generated by isotime. The string
is used in tokens and other public APIs and we can't change it
without potentially breaking clients.
So the workaround is to copy the current implementation from
oslo_utils.timeutils.isotime() to keystone.common.utils.isotime().
Closes-Bug: 1461251
Change-Id: Icf821be8cd4ee7f52c1a3d89bfed302488c080f2
386054847e