MINOR: stick-tables: limit the number of visited nodes during expiration

MINOR: stick-tables: limit the number of visited nodes during expiration

As reported by Felipe in GH issue #3084, on large systems it's not
sufficient to leave the expiration process after a certain number of
expired entries, because if they accumulate too fast, it's possible
to still spend some time visiting many (e.g. those still in use),
which takes time.

Thus here we're taking a stricter approach consisting in counting the
number of visited entries, which allows to leave early if we can't do
the expected work in a reasonable amount of time.

In order to avoid always stopping on first shards and never visiting
last ones, we're always starting from a random shard number and looping
from that one. This way even if we always leave early, all shards will
be handled equally.

This should be backported to 3.2.