Adds the check for 'not None' also when building host_info dict for ElastiCache clusters, nodes and replication groups

Adds the appropriate key checks for ElastiCache replication groups in get_dict_from_describe_dict method

Creates get_host_info_dict_from_describe_dict helper method to translate information from a 'describe' call (we don't have instance objects in this case)

Adds get_elasticache_clusters_by_region method to perform the API call to AWS (and sadly finds out that Boto support for ElastiCache is very outdated...)

Update index.rst

Adding some copy edits. Feel free to disregard.

Display a warning when using a deprecated module

open_url() is suitable for use outside of a module environment.  Will
let us use open_url to do SSL cert verification in other, non-module
code.

Require passlib over crypt in password_hash for Mac OS X/Darwin. Fixes #11244

i was almost done with my patch ... but I like yours better