build-unit-test-docker: convert to Python

Do a near identical conversion from bash to Python for the script which
builds the unit-test docker containers.  I plan to do additional
enhancements to build the sub-containers in parallel, so I needed to
first do this conversion to Python in order to make that implementation
sane.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I6df6f294b41f3a01f95fbe23a6dcd1ea21a315a9
diff --git a/jenkins/run-build-script-ci b/jenkins/run-build-script-ci
index 2c60164..3181b80 100755
--- a/jenkins/run-build-script-ci
+++ b/jenkins/run-build-script-ci
@@ -9,8 +9,8 @@
 
 export LANG=en_US.UTF8
 
-cd ${WORKSPACE}/openbmc-build-scripts
+cd "${WORKSPACE}"/openbmc-build-scripts
 
 # Now run some of our most used CI scripts
-./build-unit-test-docker.sh
+./scripts/build-unit-test-docker
 ./scripts/build-qemu-robot-docker.sh