Removed some typos

This was a followup from https://review.openstack.org/#/c/172192/

Removed the not-required in nova_server.rb and updated to the correct
bento box.

Change-Id: I73cd8e9b8bc63d8763045dcaf99f032947191f2d

.kitchen.yml

@@ -8,7 +8,7 @@ provisioner:
 platforms:
   - name: ubuntu-14.04
   - name: centos-6.6
-  - name: centos-7.0
+  - name: centos-7.1
 
 suites:
   - name: default

providers/nova_server.rb

@@ -16,9 +16,6 @@
 # limitations under the License.
 #
 
-require 'tempfile'
-require 'chef/digester'
-
 include Openstack::Client::Nova
 
 def whyrun_supported?