Grow: support consistency policy change

Grow: support consistency policy change

Extend the --consistency-policy parameter to work also in Grow mode.
Using it changes the currently active consistency policy in the kernel
driver and updates the metadata to make this change permanent. Currently
this supports only changing between "ppl" and "resync" policies, that is
enabling or disabling PPL at runtime.

Signed-off-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@gmail.com>