`DOCKER_LIMS2_IMAGE` must be defined before when it's been used.
bugfix
Merge pull request #27 from dochang/next

Fix several bugs
Checkout `$LIMS2_COMMIT` after `git clone`.

`git clone --branch` cannot checkout a plain commit id.  Use `git
checkout` instead.
Merge pull request #28 from dochang/next

Checkout `$LIMS2_COMMIT` after `git clone`.