os/bluestore: introduce a cooldown period for failed BlueFS allocations.

os/bluestore: introduce a cooldown period for failed BlueFS allocations.

When using bluefs_shared_alloc_size one might get a long-lasting state when
that large chunks are not available any more and fallback to shared
device min alloc size occurs. The introduced cooldown is intended to
prevent repetitive allocation attempts with bluefs_shared_alloc_size for
a while. The rationale is to eliminate performance penalty these failing
attempts might cause.

Signed-off-by: Igor Fedotov <igor.fedotov@croit.io>
(cherry picked from commit e52bcc852ce51ab99138420f9069e2f59e1cb706)