exec: Override container process option if needed
exec: Override container process option if needed

runc expects the exec command to use the same options defined when
the container process was started. And if the command line provide
some options, we should override with what is provided.

Fixes #323

Signed-off-by: Sebastien Boeuf <90b401417360b1924ef3f520ddee932686110f85@intel.com>

clearcontainers/runtime,devimc/runtime,chavafg/runtime,clearcontainers/runtime,devimc/runtime,chavafg/runtime