Add input processing to Packer for shell interpolation

Issue #88

* Added to_command_hash_elements to allow processing packers inputs.
* Now interpolation of shell commands will function as expected in packer.
* Leveraged mainly for generating aws keys in template to allow seemless role assumption for provisioners and builders.

lib/covalence/core/entities/input.rb

@@ -28,6 +28,10 @@ def to_command_option
       "#{name} = #{parse_input(value())}"
     end
 
+    def to_command_hash_elements
+       return name, parse_input(value()).delete_prefix('"').delete_suffix('"')
+    end
+
     private
 
     def get_value(input)

lib/covalence/core/entities/stack.rb

@@ -51,8 +51,8 @@ def materialize_cmd_inputs(path)
         File.open("#{path}/covalence-inputs.tfvars",'w') {|f| f.write(config)}
       elsif type == "packer"
         config = Hash.new
-        inputs.each do |name, input|
-          config[name] = input.value
+        inputs.values.map(&:to_command_hash_elements).each do |name, input|
+          config["#{name}"] = input
         end
         config_json = JSON.generate(config)
         logger.info "path: #{path} module_path: #{module_path}\nStack inputs:\n\n#{config_json}"