Description of problem:
Currently when deploying BlueStore OSD's using the non-colocated OSD scenario (ceph-disk) we will create ceph block.wal by default. We should not be creating block.wal unless THREE tiers of storage are being used, HDD, SSD and NVDIMM for example.  

The playbook does have the option to use 'bluestore_wal_devices', could we ONLY create the block.wal if this parameter is populated with a device and change the default to ONLY create ceph block.db and ceph data?

Version-Release number of selected component (if applicable):
RHCS 3.2

How reproducible:
Constant

Steps to Reproduce:
1. Deploy a BlueStore OSD using Ceph-Ansible and the non-collocated scenario.

Actual results:
In non-collocated scenario we create ceph data, ceph block.db and ceph block.wal. 

[root@ceph6 ~]# lsblk
sdb                   8:16   0 111.8G  0 disk 
├─sdb5                8:21   0     1G  0 part 
└─sdb6                8:22   0   576M  0 part 
sdc                   8:32   0 465.8G  0 disk 
├─sdc1                8:33   0   100M  0 part /var/lib/ceph/osd/ceph-2
└─sdc2                8:34   0 465.7G  0 part 

[root@ceph6 ~]# blkid /dev/sdc*
/dev/sdc: PTTYPE="gpt" 
/dev/sdc1: UUID="d1d98c71-61ae-42f0-98e0-b6fb64930044" TYPE="xfs" PARTLABEL="ceph data" PARTUUID="0b88f43d-f7d3-4326-ba96-b1d8c2a41684" 
/dev/sdc2: PARTLABEL="ceph block" PARTUUID="bb1d67ca-5fc1-438f-936a-e32c54bfac36" 

[root@ceph6 ~]# blkid /dev/sdb*
/dev/sdb5: PARTLABEL="ceph block.db" PARTUUID="e2376d5c-f42b-4e59-aa79-b789bdc43cef" 
/dev/sdb6: PARTLABEL="ceph block.wal" PARTUUID="b60c1235-5c8e-4e1e-8704-7b4e49061197"


Expected results:
We should only be deploying ceph block and block.db.

Additional info: