Configure write cache option of tgtd iscsi driver

Cinder LVMiSCSI driver is using default value of write-cache parameter
of tgtd iscsi driver. In this setting, write I/O from guest instance is
cached on dirty cache of a host.(write-back mode)

In this case, data lost may be occurred if the host crashes before
flushing dirty cache. This may cause a lot of instances to lose
their data.

In order to avoid this issue, it is better to turn off the write cache.
(write-through mode)

This patch adds "iscsi_write_cache" parameter to configure a behavior of
write cache. The default value is "iscsi_write_cache=on".(write-back mode)

Closes-Bug: 1336568
DocImpact

Change-Id: I7a495bc6118d4254576bdf1620a04ac537b3078d
Signed-off-by: Mitsuhiro Tanino <mitsuhiro.tanino@hds.com>
Fix failure of source volume deletion in migrate_volume_completion

In VolumeManager.migrate_volume_completion(), when volume_status is not
'retyping', status_update is not set. However, status_update is always
referenced as dictionary on volume deletion path, so it fails to delete
migration source volume. This patch fixes the issue.

Change-Id: I06889dae326b9557e044f1712d9f3205bb68a953
Closes-Bug: 1344341
Add additional explicit imports of _ where needed

It appears that I missed some of the needed explicit
imports of _.  I have now run through all the /bin/cinder-*
functions and ensured that they can be properly started.

This patch adds additional imports of _ and also changes
cinder-rtstool to use the 'cinder' domain as was suggested by
Duncan Thomas in the first review cycle.

Change-Id: I6477093cb817b5b9506dd3787f027e073c51f37d
Closes-Bug:  1345789
Switch to use oslo.db

oslo.db first stable release has been cut and we can start using it
instead of openstack/common/db/* code which is now marked obsolete.

Change-Id: Ib350e8d1dcec3be707e3b1679c70202619256269
Merge "Add additional explicit imports of _ where needed"
Merge "Fix failure of source volume deletion in migrate_volume_completion"
Merge "Configure write cache option of tgtd iscsi driver"