add provider argument to eos shared module

Adds a new argument `provider` to the eos shared module and updates the
eos doc fragment.  This commit includes some additional minor fixes and
code refactors for naming conventions.  The `provider` argument allows the
shared module arguments to be passed as a dict object instead of having
to pass each argument invididually.

lib/ansible/utils/module_docs_fragments/eos.py

@@ -80,5 +80,12 @@ options:
     required: false
     default: true
     choices: BOOLEANS
+  provider:
+    description:
+      - Convience method that allows all M(eos) arguments to be passed as
+        a dict object.  All constraints (required, choices, etc) must be
+        met either by individual arguments or values in this dict.
+    required: false
+    default: null
 
 """