GlusterFS volume mount should check for O_DIRECT support

[Eric Harney]

From https://ask.openstack.org/question/758 :

GlusterFS mounts on older platforms (i.e. Ubuntu 12.04) don't support O_DIRECT, and fail because driver_cache = "none" is set by LibvirtBaseVolumeDriver.

The instance store LibvirtDriver has a check for this which sets disk_cachemode to "writethrough" if O_DIRECT is not supported. The volume mounting code should do a similar check and set the option accordingly.

[Jeffrey Zhang (jeffrey4l)]

It seems that when using libgfapi [1], this bug is still exist.

[1] https://blueprints.launchpad.net/nova/+spec/glusterfs-native-support

[Markus Zoeller (markus_z) (mzoeller)]

This is an automated cleanup. This bug report has been closed because it
is older than 18 months and there is no open code change to fix this.
After this time it is unlikely that the circumstances which lead to
the observed issue can be reproduced.

If you can reproduce the bug, please:
* reopen the bug report (set to status "New")
* AND add the detailed steps to reproduce the issue (if applicable)
* AND leave a comment "CONFIRMED FOR: <RELEASE_NAME>"
  Only still supported release names are valid (LIBERTY, MITAKA, OCATA, NEWTON).
  Valid example: CONFIRMED FOR: LIBERTY