Fix hard-coded etcd cluster size

[hongbin]

In before, the etcd cluster size was hard-coded to 1, and there is a TODO item to fix the hard-coded size [1]. Now, it's time to fix it. We should use the number of master nodes as the size of the etcd cluster.

[1] https://review.openstack.org/#/c/204366/10/magnum/conductor/template_definition.py

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/219896

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/219896
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=c6c4053d957da366405546f1651af9e75fa754a7
Submitter: Jenkins
Branch: master

commit c6c4053d957da366405546f1651af9e75fa754a7
Author: Hongbin Lu <email address hidden>
Date: Wed Sep 2 18:07:50 2015 -0400

    Fix the hard-coded etcd cluster size

    In before, the etcd cluster size was hard-coded to 1, since HA mode
    hadn't been implemented at that time. Now, we fix it. The etcd
    cluster size is set to the number of master nodes.

    Change-Id: I198ca604401bc805f31e8187f5245177761edf56
    Closes-Bug: #1491602