Description of problem:
While working to resole bug 1536214 to get the VDO Ansible module working again, I found that an attempt to change the write policy fails due to the error "unrecognized arguments: --writePolicy=async".  This was previously successful, but is no longer a valid option (this is detailed in bug 1536166).

Version-Release number of selected component (if applicable):
vdo-6.1.0.114-14.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Install the vdo.py ansible module to the Ansible ".../modules/system" subdirectory of the system to run VDO, and a control system.
2. Copy one of the example playbooks from the /usr/share/doc/vdo/examples/ansible directory of the system with VDO to the control system, and create a playbook that uses a local username, acts on a block device existing on the system, and has various other parameters.  

Recommended sequence: use /usr/share/doc/vdo/examples/ansible/test_vdocreate.yml as a base for a creation playbook, /usr/share/doc/vdo/examples/ansible/test_vdoremove.yml as a base for a removal playbook, and a version of /usr/share/doc/vdo/examples/ansible/test_vdocreate.yml with the additional line "writepolicy: async" to act as a playbook to modify the write policy to async.

3. On the control system, after passwordless ssh has been established, execute "ansible-playbook <playbook_filename.yml>".

Actual results:
The ansible-playbook command fails with error output similar to the output below (from the resulting equivalent command "vdo modify --name=vdo1 --writePolicy=async"):
usage: vdo modify [-h] (-a | -n <volume>) [--blockMapCacheSize <megabytes>]
                  [--blockMapPeriod <period>] [--readCache {disabled,enabled}]
                  [--readCacheSize <megabytes>]
                  [--vdoAckThreads <threadCount>]
                  [--vdoBioRotationInterval <ioCount>]
                  [--vdoBioThreads <threadCount>]
                  [--vdoCpuThreads <threadCount>]
                  [--vdoHashZoneThreads <threadCount>]
                  [--vdoLogicalThreads <threadCount>]
                  [--vdoPhysicalThreads <threadCount>] [-f <file>]
                  [--logfile <pathname>] [--verbose]
vdo modify: error: unrecognized arguments: --writePolicy=async


Expected results:
The ansible-playbook command succeeds with "changed=1", and the VDO volume's write policy is successfully changed to the destination write policy.

Additional info: