etcd3 as a base service

ETCD_DOWNLOAD_URL is set to github url, in our CI, we can point
ETCD_DOWNLOAD_URL to a url in tarballs.openstack.org possibly
in devstack-gate

Download the etcd binaries and drop them into /opt/stack/bin and
use it from there. Cache the tgz for subsequent use (local workflow)

daemon-reload is called twice once from inside the write_user_unit_file
and then when we adjust the entries with additional things recommended
by the etcd team. We need a better way to do this in the future.

Added a TODO to verify the downloaded artifact later. The etcd team
posts gpg signature, we could verify that or run sha256sum and hard
code that in lib/etcd3 file. We would have to update it whenever we
bump the etcd3 version.

We use the public key "CoreOS Application Signing Key <security@coreos.com>"
with ID FC8A365E to verify the integrity of the downloaded file

Any jobs that need to be run on architectures where v3.1.7 is not available
should rey the v3.2.0-rcX release candidates. We can switch to v3.2.0
when it gets released.

Initial version of this code was borrowed from the dragonflow
repo:
http://git.openstack.org/cgit/openstack/dragonflow/tree/devstack

Change-Id: Ibbb430fb1dbf66942168e0cb52d990ab6a2eb8d7

unstack.sh

@@ -69,6 +69,7 @@ source $TOP_DIR/lib/swift
 source $TOP_DIR/lib/neutron
 source $TOP_DIR/lib/ldap
 source $TOP_DIR/lib/dstat
+source $TOP_DIR/lib/etcd3
 source $TOP_DIR/lib/dlm
 
 # Extras Source
@@ -162,6 +163,11 @@ if is_service_enabled neutron; then
     cleanup_neutron
 fi
 
+if is_service_enabled etcd3; then
+    stop_etcd3
+    cleanup_etcd3
+fi
+
 if is_service_enabled dstat; then
     stop_dstat
 fi