Make pip_install honour pip_install_options

Add a pip_install_options variable to the extra_args parameter of
the Ínstall pip packages task.

The variable is set to a default value of "" in the roles default
variables.

Change-Id: I3ffead4f63c85215c2d6b6fec5a02837cc7f7551
Closes-Bug: 1620872

defaults/main.yml

@@ -66,3 +66,11 @@ pip_links: []
 
 ## Tunable overrides
 pip_global_conf_overrides: {}
+
+## Additional options to pass to pip
+# Example:
+#   pip_install_options: "--cert /etc/ssl/certs/ca-certificates.crt"
+#
+# See the documentationat https://pip.pypa.io/en/stable/reference/pip
+# for details.
+pip_install_options: ""

tasks/install_source.yml

@@ -39,7 +39,7 @@
   pip:
     name: "{{ pip_required_pip_packages | map('quote') | join(' ') }}"
     state: latest
-    extra_args: "{{ (pip_install_fall_back | changed) | ternary('--isolated', '') }}"
+    extra_args: "{{ (pip_install_fall_back | changed) | ternary('--isolated', '') }} {{ pip_install_options }}"
   register: install_packages
   until: install_packages|success
   retries: 5