This check does not require manually setting the number of expected
OSDs.
Initially, the charm sets the count (per-host) to that of what's
present in the OSD tree. The count will be updated (on a per-host
basis) when the number of OSDs grows, but not when it shrinks. There
is a charm action to reset the expected count using information from
the OSD tree.
Closes-Bug: #1952985
Change-Id: Ia6a060bf151908c1d4159e6bdffa7bfe1f0a7988
b8af44aefa