[libzookeeper] Make sure that ensemble list is converted to a string

ensemble=localhost:2181,localhost:2182,localhost:2183
will create a list
['localhost:2181', 'localhost:2182', 'localhost:2183']

While
ensemble="localhost:2181,localhost:2182,localhost:2183"
will stay as a string
"localhost:2181,localhost:2182,localhost:2183"

Conflicts:

	desktop/libs/libzookeeper/src/libzookeeper/conf.py
	desktop/libs/libzookeeper/src/libzookeeper/tests.py

Branch for CDH5.3.6

HUE-2814 Revert "[desktop] Remove pyopenssl version 0.13"

This reverts commit 907510d.

Branch for CDH5.2.6

Branch for CDH5.3.5

Branch for CDH5.4.3

Branch for CDH5.4.2