build-helm-charts.sh now requires python-yaml

[Scott Little]

Brief Description
-----------------
build-helm-charts.sh fails when used within docker
due to missing python-yaml package

Severity
--------
Critical: Can't build helm charts

Steps to Reproduce
------------------
1) enter docker build environment
2) build-helm-charts.sh

Expected Behavior
------------------
Command loads, complains about missing arguements

Actual Behavior
----------------
python throws an exception on 'import yaml'

Reproducibility
---------------
Reproducible, 100%

System Configuration
--------------------
N/A

Branch/Pull Time/Commit
-----------------------
20190607T013000Z

Last Pass
---------
20190604T144018Z

Timestamp/Logs
--------------
00:37:12 Traceback (most recent call last):
00:37:12 File "<string>", line 3, in <module>
00:37:12 ImportError: No module named yaml

Test Activity
-------------
Build

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/663983
Committed: https://git.openstack.org/cgit/starlingx/tools/commit/?id=d351bd4b3dec12a86fdb9bdaaa468aeb69e0b735
Submitter: Zuul
Branch: master

commit d351bd4b3dec12a86fdb9bdaaa468aeb69e0b735
Author: Scott Little <email address hidden>
Date: Fri Jun 7 11:39:52 2019 -0400

    build-helm-charts.sh now requires python-yaml

    A recent change, https://review.opendev.org/#/c/662087/ ,
    added 'import yaml' to build-helm-charts.sh. However
    the docker build environmnet does not include python-yaml
    in it's Dockerfile.

    This update adds the missing python-yaml to the Dockerfile

    Change-Id: Ia446bc587efb4b1997008661a4b584183891bb4f
    Closes-Bug: 1832017
    Signed-off-by: Scott Little <email address hidden>