CooperativeReader not py3-ready

[Brian Rosmaita]

Tim Burke noticed this in IRC today:
https://github.com/openstack/glance_store/blob/0.28.0/glance_store/common/utils.py#L138

In the CooperativeReader class:
    def read(self, length=None):
        """Return the next chunk of the underlying iterator.

        This is replaced with cooperative_read in __init__ if the underlying
        fd already supports read().
        """
        if self.iterator is None:
            self.iterator = self.__iter__()
        try:
            return next(self.iterator)
        except StopIteration:
            return ''

This needs to return b''.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/651941
Committed: https://git.openstack.org/cgit/openstack/glance_store/commit/?id=0a3166558f1b2f382075145502576919cecec61e
Submitter: Zuul
Branch: master

commit 0a3166558f1b2f382075145502576919cecec61e
Author: Cyril Roelandt <email address hidden>
Date: Fri Apr 12 01:40:04 2019 +0200

    Python3: Fix return type on CooperativeReader.read

    CooperativeReader.read() should return bytes. A similar change was
    merged in Glance.

    Change-Id: Iee3b49235be2af64eac3933e41c7e44fc1a564f4
    Closes-Bug: #1818915

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/glance_store 0.29.0 release.