Optimise pip install tasks

Unlike the Ansible apt module, the Ansible pip module does not
recognise a with_items list and process all the items at once.

To optimise the pip install tasks, this patch replaces the use
of with_items with a join filter so that the pip install task
does an install with all the packages in a list, ensuring that
the execution is one action instead of many.

Change-Id: I9a372286efe2105568f9ef2d29be62d0f8070303

tasks/sahara_install.yml

@@ -64,14 +64,13 @@
 
 - name: Install required pip packages
   pip:
-    name: "{{ item }}"
+    name: "{{ sahara_required_pip_packages | join(' ') }}"
     state: present
     extra_args: "{{ pip_install_options_fact }}"
   register: install_packages
   until: install_packages|success
   retries: 5
   delay: 2
-  with_items: "{{ sahara_required_pip_packages }}"
   tags:
     - sahara-install
     - sahara-pip-packages
@@ -160,7 +159,7 @@
 
 - name: Install pip packages (venv)
   pip:
-    name: "{{ item }}"
+    name: "{{ sahara_pip_packages | join(' ') }}"
     state: present
     virtualenv: "{{ sahara_bin | dirname }}"
     virtualenv_site_packages: "no"
@@ -169,7 +168,6 @@
   until: install_packages|success
   retries: 5
   delay: 2
-  with_items: "{{ sahara_pip_packages }}"
   when:
     - sahara_get_venv | failed or sahara_developer_mode | bool
   notify: