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: Iaca857cbc31a915b8fdecfe4a06f5afb5abb46bf

tasks/horizon_install.yml

@@ -51,14 +51,13 @@
 
 - name: Install requires pip packages
   pip:
-    name: "{{ item }}"
+    name: "{{ horizon_requires_pip_packages | join(' ') }}"
     state: latest
     extra_args: "{{ pip_install_options_fact }}"
   register: install_packages
   until: install_packages|success
   retries: 5
   delay: 2
-  with_items: "{{ horizon_requires_pip_packages }}"
 
 - name: Get local venv checksum
   stat:
@@ -125,7 +124,7 @@
 
 - name: Install pip packages
   pip:
-    name: "{{ item }}"
+    name: "{{ horizon_pip_packages | join(' ') }}"
     state: latest
     virtualenv: "{{ horizon_bin | dirname }}"
     virtualenv_site_packages: "no"
@@ -134,7 +133,6 @@
   until: install_packages|success
   retries: 5
   delay: 2
-  with_items: "{{ horizon_pip_packages }}"
   when:
     - horizon_get_venv | failed or horizon_developer_mode | bool
   notify: Restart apache2