Do not start chef-solo if mso-docker.json is empty

Do not start chef-solo if mso-docker.json is empty

Chef-solo is started both from the docker container [1] and from
the start-jboss-server.sh script [2].
The Dockerfile is configured to erase the mso-docker.json
configuration once applied, so when the container is started,
and the strat-jboss-server.sh tries to play the recipes again,
it fails as the environment file is empty.

This patch adds a check to see if the file is empty, if not, we
play the chef-solo recipes again, to overwrite the config.

[1]: https://gerrit.openecomp.org/r/gitweb?p=mso.git;a=blob;f=packages/docker/src/main/docker/docker-files/Dockerfile.mso-chef-final;h=ff7f44bcfdba6fa0328cbd50803d3dc80a2a1def;hb=refs/heads/master#l57
[2]: https://gerrit.openecomp.org/r/gitweb?p=mso.git;a=blob;f=packages/docker/src/main/docker/docker-files/scripts/start-jboss-server.sh;h=2e9b9da27dd3d01fcf5ebc304ac03b15142fde53;hb=refs/heads/master#l16

Change-Id: I34573dedaaafbeb6b511f47b72e6e0cefea4e1d5
Signed-off-by: Alexis de Talhouët <adetalhouet89@gmail.com>