Cap elasticsearch client <2.0
Cap elasticsearch client <2.0

The elasticsearch 2.0 python client is not backwards compatible
with 1.x, nor with server versions prior to 2.0 (and similarly, the
1.x client cannot be used with server versions after 1.x).

See https://elasticsearch-py.readthedocs.org/en/master/ for details.
Since devstack installs elasticsearch 1.x it seems sensible to cap
the client version. Deployers using version 2.0 will need to install
that client version in projects requiring it.

Note: Autoproposal bot isn't enabled yet or this would have trickled
from Steve McLellan's patch:

https://review.openstack.org/#/c/252075/

Change-Id: I7f5a6a74968980636c340e2d059a70b508ece0fc
Partial-Bug: #1515412
Co-Authored-By: Steve McLellan <fa4f5a82adc8a51aae582e7267bacdfa33c25c8e@gmail.com>

openstack/searchlight,openstack/searchlight,openstack/searchlight