Don't install python-yaml package

PyYAML is already a dependency of diskimage-builder, so the distro
package doesn't need to be installed explicitly. If it is installed by
the distro, then on a system with pip 10 the DIB installation will fail.

Change-Id: Ibbd69930f8282fe9b7daef9808db3219a0f67ced

manifests/init.pp

@@ -58,13 +58,6 @@ class diskimage_builder (
     ensure  => present,
   }
 
-  # required by the diskimage-builder element scripts
-  if ! defined(Package['python-yaml']) {
-      package { 'python-yaml':
-          ensure => present,
-      }
-  }
-
   # required by lvm dib element
   if ! defined(Package['lvm2']) {
       package { 'lvm2':
@@ -80,7 +73,6 @@ class diskimage_builder (
       source   => $git_source_repo,
       require  => [
         Class['pip'],
-        Package['python-yaml'],
       ],
     }
   }
@@ -90,7 +82,6 @@ class diskimage_builder (
       provider => openstack_pip,
       require  => [
         Class['pip'],
-        Package['python-yaml'],
       ],
     }
   }

spec/acceptance/basic_spec.rb

@@ -35,7 +35,6 @@ describe 'puppet-diskimage_builder module', :if => ['debian', 'ubuntu'].include?
         package('debootstrap'),
         package('kpartx'),
         package('python-lzma'),
-        package('python-yaml'),
         package('qemu-utils'),
         package('ubuntu-keyring'),
         package('vhd-util'),