Upstream: suppressed the file cache slab allocator error messages.
Upstream: suppressed the file cache slab allocator error messages.

The messages "ngx_slab_alloc() failed: no memory in cache keys zone"
from the file cache slab allocator are suppressed since the allocation
is likely to succeed after the forced expiration of cache nodes.
The second allocation failure is reported.

hy0kl/nginx,firebase/nginx,firebase/nginx,firebase/nginx,hy0kl/nginx,hy0kl/nginx,firebase/nginx