Reduce memory consumption in Cinder services

This patch reduces memory usage on the Cinder Volume and Backup services
by tuning glibc.

The specific tuning consist on disabling the per thread arenas and
disabling dynamic thresholds.

The Cinder Backup service suffers from high water mark memory usage and
uses excessive memory.  As an example just after 10 restore operations
the service uses almost 1GB of RAM and does not ever free it afterwards.
With this patch the memory consumption of the service is reduced down to
almost 130MB.  If we add a revert from Cinder (Change-Id
I43a20c8687f12bc52b014611cc6977c4c3ca212c) it goes down to 100MB during
my tests.

This glibc tuning is not applied to all Python services because I
haven't done proper testings on them and at first glance they don't seem
to have such great improvements.

Related-bug: #1908805
Change-Id: Ic9030d01468b3189350f83b04a8d1d346c489d3c
2 files changed