Add LVM NVMe support

This patch adds NVMe LVM support to the existing iSCSI LVM configuration
support.

We deprecate the CINDER_ISCSI_HELPER configuration option since we are
no longer limited to iSCSI, and replace it with the CINDER_TARGET_HELPER
option.

The patch also adds another 3 target configuration options:

- CINDER_TARGET_PROTOCOL
- CINDER_TARGET_PREFIX
- CINDER_TARGET_PORT

These options will have different defaults based on the selected target
helper.  For tgtadm and lioadm they'll be iSCSI,
iqn.2010-10.org.openstack:, and 3260 respectively, and for nvmet they'll
be nvmet_rdma, nvme-subsystem-1, and 4420.

Besides nvmet_rdma the CINDER_TARGET_PROTOCOL option can also be set to
nvmet_tcp, and nvmet_fc.

For the RDMA transport protocol devstack will be using Soft-RoCE and
creating a device on top of the network interface.

LVM NVMe-TCP support is added in the dependency mentioned in the footer
and LVM NVMe-FC will be added in later patches (need os-brick and cinder
patches) but the code here should still be valid.

Change-Id: I6578cdc27489b34916cdeb72ba3fdf06ea9d4ad8
6 files changed