Set ETCD_USE_RAMDISK=True by default

Cinder and etcd are enabled by default and by default
cinder uses etcd as a distributed lock manager with
tooz as an intermediary. We see a lot of ToozConnectionErrors [1]
in the cinder logs when etcd is backed up [2] which results in
cinder operations timing out causing test failures, like
when a volume is not deleted within a given time.

This changes ETCD_USE_RAMDISK=True by default to try and
alleviate some of the pressure. An alternative is if we know
we're in a single-node job we could just not use a DLM for
Cinder.

[1] http://status.openstack.org/elastic-recheck/#1810526
[2] etcd[26824]: sync duration of 12.076762123s, expected less than 1s

Change-Id: I5f82aa40e9d84114e7b7b5cf19ec4942d6552490
Partial-Bug: #1810526

Author: mriedem

lib/etcd3

@@ -29,7 +29,7 @@ ETCD_SYSTEMD_SERVICE="devstack@etcd.service"
 ETCD_BIN_DIR="$DEST/bin"
 # Option below will mount ETCD_DATA_DIR as ramdisk, which is useful to run
 # etcd-heavy services in the gate VM's, e.g. Kubernetes.
-ETCD_USE_RAMDISK=$(trueorfalse False ETCD_USE_RAMDISK)
+ETCD_USE_RAMDISK=$(trueorfalse True ETCD_USE_RAMDISK)
 ETCD_RAMDISK_MB=${ETCD_RAMDISK_MB:-512}
 
 if is_ubuntu ; then