Remove join filter from optional pip module tasks

Ansible 2.2 now treats the 'name' argument for the pip module
as a list, removing the need for us to implement the join
filter to optimise the install execution.

Change-Id: I16d6d75cc432ba57407689d0e1a4055c8172ce12

tasks/swift_pypy_setup.yml

@@ -55,7 +55,7 @@
 
 - name: Install pip packages into pypy venv
   pip:
-    name: "{{ swift_pip_packages | join(' ') }}"
+    name: "{{ swift_pip_packages }}"
     state: "{{ swift_pip_package_state }}"
     virtualenv: "{{ swift_bin | dirname }}"
     virtualenv_site_packages: "no"