Expose the resume functionality through a specific CLI command

Fixes #57

features/cli/resume.feature

@@ -0,0 +1,17 @@
+Feature: Resume a VM or VMs that were previously stopped
+
+  Scenario: Resume without stopped Blimps
+    Given I have the Blimpfile:
+      """
+        Blimpy.fleet do |f|
+          f.add(:aws) do |host|
+            host.name = 'Cucumber Host'
+          end
+        end
+      """
+    When I run `blimpy resume`
+    Then the exit status should be 1
+    And the output should contain:
+      """
+      No fleet running right now, perhaps you should `start` one.
+      """

lib/blimpy/cli.rb

@@ -52,17 +52,25 @@ module Blimpy
         end
         data
       end
+
+      def load_fleet
+        ensure_blimpfile
+        begin
+          return load_blimpfile
+        rescue Blimpy::InvalidBlimpFileError => e
+          puts "The Blimpfile is invalid!"
+          puts e.to_s
+          return nil
+        end
+      end
     end
 
     desc 'start', 'Start up a fleet of blimps'
     method_options :"dry-run" => :boolean
     def start
-      ensure_blimpfile
-      begin
-        fleet = load_blimpfile
-      rescue Blimpy::InvalidBlimpFileError => e
-        puts "The Blimpfile is invalid!"
-        puts e.to_s
+      fleet = load_fleet
+
+      if fleet.nil?
         exit 1
       end
 
@@ -74,6 +82,22 @@ module Blimpy
       fleet.start
     end
 
+    desc 'resume', 'Resume an existing fleet of instances'
+    def resume
+      fleet = load_fleet
+
+      if fleet.nil?
+        exit 1
+      end
+
+      if fleet.members.empty?
+        puts "No fleet running right now, perhaps you should `start` one."
+        exit 1
+      else
+        fleet.resume(fleet.members)
+      end
+    end
+
     desc 'show', 'Show blimp details for running blimps'
     method_options :tags => :boolean
     def show