Delegate default command to the entrypoint script
this allow a better handling of the environment for the default command (shell) or user command (that may be something like bash -c '...'
).
For example
$ lb-docker-run --docker-prefix gitlab-registry.cern.ch/clemenci/lbdocker --update --quiet-env --lbenv-testing bash -c 'which lb-run'
v4: Pulling from clemenci/lbdocker/centos7-build
Digest: sha256:523662dd589800c9ef2073a4bfd243d574310d196b6b6e3da21d251567d1a0d6
Status: Image is up to date for gitlab-registry.cern.ch/clemenci/lbdocker/centos7-build:v4
/cvmfs/lhcb.cern.ch/lib/var/lib/LbEnv/448/stable/x86_64-centos7/bin/lb-run
Closes #3 (closed)