Optimise pip install tasks
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: Ib9ce9666c737be639825a5b998f57eaca4a25c7d

os-cloud/openstack-ansible-lxc_hosts,openstack/openstack-ansible-lxc_hosts,openstack/openstack-ansible-lxc_hosts,os-cloud/openstack-ansible-lxc_hosts