There are currently 8 places in CockroachDB non-test code
that create a `time.Timer` using `time.NewTimer` during
every iteration of a loop. cockroachdb#4175 proposed a fix for the worst
instance of this issue within `*rpcTransport.processQueue`,
which resulted in upwards of **400,000** timers on a single node
inuse at a given time. The second biggest offender of this
issue was in `kv.send`, which resulted in about **30,000** timers
on a single node inuse at a given time. Together, I diagnosed
that these two issues were responsible for the memory "leak"
seen in cockroachdb#4346. After making these fixes, it looks like the
issue is gone as memory no longer grows without bound.

I've gone ahead and fixed all 8 occurences of this anti-pattern
across our codebase, using the strategy @tamird brought up in
[this](https://github.com/cockroachdb/cockroach/pull/4175/files#r52558817)
comment
to avoid a race condition between iterations with the timers.
A few of the changes might be a little over-aggressive as the
loops are not as "tight" as the ones causing issues, but I still
think it's important to make this change now and avoid these
issues in the future.