By default, etcd makes a huge 10 GB mmap() allocation when it starts up.
It doesn't actually use that much memory, it's just address space, but
it caused me grief when I tried to use 'rr' to debug a python test run.
Apparently, when you replay the 'rr' trace, it does allocate memory for
all that address space.
The size of the initial mmap depends on the --quota-backend-bytes setting.
Our etcd clusters are very small, so let's set --quota-backend-bytes to
keep the virtual memory size small, to make debugging with 'rr' easier.
See https://github.com/etcd-io/etcd/issues/7910 and
5e4b008106
