fix: split client.sls into distinct, dedicated SLS files

Additionally export a `constants` dict from the `map.jinja` to handle
any shared or verbose constants — such as file paths, environment
variables, etc… — and make the individual SLS files more concise. Also,
fix a minor logic issue introduced in commit c42a332 that would not
reference the kubectl configuration managed by this formula if the
kubectl binary is not installed by the formula.

Fixes salt-formulas/salt-formula-helm#8
diff --git a/README.rst b/README.rst
index b3e830f..91bb364 100644
--- a/README.rst
+++ b/README.rst
@@ -18,14 +18,9 @@
 _The following examples demonstrate configuring the formula for different
 use cases._
 
-Enable formula, install helm client on node and tiller on Kubernetes (assuming
-already configured kubectl config or local cluster endpoint):
-
-.. code-block:: yaml
-
-    helm:
-      client:
-        enabled: true
+The default pillar configuration will install the helm client on the target 
+node, and Tiller to the Kubernetes cluster (assuming kubectl config or local 
+cluster endpoint have already been configured.
 
 Change version of helm being downloaded and installed: