There is no way to change etcd checksum

[Shachar Snapiri]

In the stackrc file, the ETCD_VERSION may be overridden by the user, but the checksum is a constant, so if the version is changed, the stack.sh will fail as there will be mismatch between the checksums.
It should be also possible to specify a different checksum

Note: Though it is possible to override ETCD_SHA256, there is infrastructure for multiple platforms, in which case you can not override the value per-platform.
This patch allows that.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/526053

[OpenStack Infra (hudson-openstack)]

Change abandoned by Shachar Snapiri (<email address hidden>) on branch: master
Review: https://review.openstack.org/526053

[Shachar Snapiri (snapiri)]

It is possible to achieve it by using the ETCD_SHA256

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/526053
Committed: https://git.openstack.org/cgit/openstack-dev/devstack/commit/?id=fabaa991ca28a181909b420701bbd8e195177814
Submitter: Zuul
Branch: master

commit fabaa991ca28a181909b420701bbd8e195177814
Author: Shachar Snapiri <email address hidden>
Date: Wed Dec 6 14:45:06 2017 +0200

    Added the ability to specify checksum for etcd

    It is possibe for the user to override te etcd version, thus download a
    different etcd file, but the checksum is constant, so the checksum
    verification will fail in that case.
    Added the ability to specify a different checksum, so the user would be
    able to specify the new version checksum

    Change-Id: I85af3af841ae957964f18d4e37a86ab0703882bc
    Closes-Bug: #1736718