src/ceph-volume: fast device unavailable as error

src/ceph-volume: fast device unavailable as error

Normally when fast devices are passed to batch command but
no fast allocations could be found the batch command will
do nothing and return an empty plan. This leads to issues
however because the return essentially makes this issue silent
which makes it hard to debug in certain scenarios. I propose
to change this to raise error, and have made changes in osd.py
to better log the errors and process the exceptions. This
shouldn't affect processes that much and the change in
osd.py ensures the raised errors will not interrupt the return
output. I've also changed the unit tests to account for
change.

Signed-off-by: Timothy Q Nguyen <timqn22@gmail.com>