Add support for API paging with limit and continue

Implement API chunking support as specified in
https://kubernetes.io/docs/reference/using-api/api-concepts/#retrieving-large-results-sets-in-chunks

Add limit and continue as parameters to get_entities and get_entities
and add continue as an optional attribute (default to nil) to
EntityList.

Fixes: ManageIQ#283

lib/kubeclient/common.rb

@@ -37,7 +37,9 @@ module ClientMixin
 
     SEARCH_ARGUMENTS = {
       'labelSelector' => :label_selector,
-      'fieldSelector' => :field_selector
+      'fieldSelector' => :field_selector,
+      'limit'         => :limit,
+      'continue'      => :continue,
     }.freeze
 
     WATCH_ARGUMENTS = { 'resourceVersion' => :resource_version }.merge!(SEARCH_ARGUMENTS).freeze
@@ -256,6 +258,8 @@ def watch_entities(resource_name, options = {})
     #   :namespace (string) - the namespace of the entity.
     #   :label_selector (string) - a selector to restrict the list of returned objects by labels.
     #   :field_selector (string) - a selector to restrict the list of returned objects by fields.
+    #   :limit (integer) - a maximum number of items to return in each response
+    #   :continue (string) - a token used to retrieve the next chunk of entities
     #   :as (:raw|:ros) - defaults to :ros
     #     :raw - return the raw response body as a string
     #     :ros - return a collection of RecursiveOpenStruct objects
@@ -456,10 +460,14 @@ def format_response(as, body, list_type = nil)
               result.fetch('metadata', {}).fetch('resourceVersion', nil)
             end
 
+          # If 'limit' was passed save the continue token
+          # see https://kubernetes.io/docs/reference/using-api/api-concepts/#retrieving-large-results-sets-in-chunks
+          continue = result.fetch('metadata', {}).fetch('continue', nil)
+
           # result['items'] might be nil due to https://github.com/kubernetes/kubernetes/issues/13096
           collection = result['items'].to_a.map { |item| Kubeclient::Resource.new(item) }
 
-          Kubeclient::Common::EntityList.new(list_type, resource_version, collection)
+          Kubeclient::Common::EntityList.new(list_type, resource_version, collection, continue)
         else
           Kubeclient::Resource.new(result)
         end

lib/kubeclient/entity_list.rb

@@ -3,12 +3,13 @@ module Kubeclient
   module Common
     # Kubernetes Entity List
     class EntityList < DelegateClass(Array)
-      attr_reader :kind, :resourceVersion
+      attr_reader :continue, :kind, :resourceVersion
 
-      def initialize(kind, resource_version, list)
+      def initialize(kind, resource_version, list, continue = nil)
         @kind = kind
         # rubocop:disable Style/VariableName
         @resourceVersion = resource_version
+        @continue = continue
         super(list)
       end
     end