This is useful when using proxies. The default Tornado backend does not
utilize proxy environment variables and isn't able to set no_proxy variable.

Change-Id: I4a51c6fc9abe65d46ed4f3adeb30f7a25337857e

Currently the CI job fails with module not found errror.
AttributeError: 'module' object has no attribute 'check_refresh

The reason is new version of salt tries to call
salt.utils.pkg.check_refresh which is not available in 2016.11.3 but is
available in 2016.11.6.
Reference:
1. https://github.com/saltstack/salt/blob/v2016.11.3/salt/states/pkg.py
2. https://github.com/saltstack/salt/blob/v2016.11.6/salt/states/pkg.py#L1819

The fix proposed here is to use pkg.installed instead of pkg.latest.
It's not a good idea to always update salt whenever the salt state is
run, this may introduce failures unknown to the user. There is a pipeline
to update packages which should be used for updating to latest.
pkg.latest generally isn't a good way to write idempotent formulas. See
official salt docs: "Generally it is better for the installed function
to be used, as latest will update the package whenever a new package is
available."

Change-Id: I8da5c36c1613e54768993080f2514afc920c49f8