build-unit-test-docker: handle existing user/group

Ubuntu Lunar docker images contain a 'ubuntu' user and group by
default at 1000.  The current code will skip creating a user if
the gid/uid already exist but then attempt to `chown` a path to
the `{username}:{username}` that it didn't create (which fails).

Rather than do-nothing if the gid/uid already exist, use groupmod
and usermod to modify those as appropriate.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ie07146be1bd2ce9bce2aac818da2f01665dba890
1 file changed