Some unit tests don't work on MacOS

[Ivan Kolodyazhny]

os.fdatasync doesn't exist on MacOS, so we need to skip tests using it
cinder.tests.unit.targets.test_cxt_driver.TestCxtAdmDriver.test_create_iscsi_target_already_exists
--------------------------------------------------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):
      File "/Users/e0ne/src/openstack/cinder-group/cinder/.tox/py27/lib/python2.7/site-packages/mock/mock.py", line 1305, in patched
        return func(*args, **keywargs)
      File "cinder/tests/unit/targets/test_cxt_driver.py", line 134, in test_create_iscsi_target_already_exists
        portals_ips=[self.configuration.iscsi_ip_address]))
      File "cinder/volume/targets/cxt.py", line 133, in create_iscsi_target
        utils.robust_file_write(volumes_dir, vol_id, volume_conf)
      File "cinder/utils.py", line 404, in robust_file_write
        os.fdatasync(tf.fileno())
    AttributeError: 'module' object has no attribute 'fdatasync'

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/390025

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/390025
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=f1f90c8084f4dde44274d63390ddcd911dd90da0
Submitter: Jenkins
Branch: master

commit f1f90c8084f4dde44274d63390ddcd911dd90da0
Author: Ivan Kolodyazhny <email address hidden>
Date: Sat Oct 22 23:55:58 2016 +0300

    Skip unit-tests which use os.fdatasync on MacOS

    MacOS doesn't have os.fdatasync so we have to skipp tests which use it.

    Change-Id: I9a93de3069b097868ab722af9a7f08d4e0d77a53
    Closes-Bug: #1635884

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/cinder 10.0.0.0b1 development milestone.