[Docker] Docker image doesn't report testing tool version

[garethsb]

CONFIG['VERSION'] is the Git repo revision hash when running the testing tool from a git clone... but run from the Docker image it's just the string 'Unknown' 😞

[garethsb]

This doesn't work:

nmos-testing/nmostesting/NMOSTesting.py

Line 1115 in bf723e8

TOOL_VERSION = repo.git.rev_parse(repo.head.object.hexsha, short=7)

We probably need to inject a build-arg, turn it into an environment variable and use that if it's present?

https://stackoverflow.com/a/63178429

[garethsb]

Fixed by #789