DefaultCreateCommand supports command w/ flags

namespaces.DefaultCreateCommand prepends the user-supplied command to
execute with "--", so that "nsinit init" does not attempt to interpret
it.

Docker-DCO-1.1-Signed-off-by: Bernerd Schaefer <bj.schaefer@gmail.com> (github: bernerdschaefer)
Merge pull request #136 from bernerdschaefer/nsinit-exec-with-flags

DefaultCreateCommand supports command w/ flags