exit: Ignore ExitError error type
exit: Ignore ExitError error type

When the agent waits for a process, if the process
terminates with an exit code different to 0, the
function will return an error of type ExitError.
The process exit code is not relevant for the
agent, lets ignore that error type.

Fixes: #146

Signed-off-by: Jose Carlos Venegas Munoz <821ab150128e889cb3ad9aab6e72689fd9ad26f2@intel.com>

clearcontainers/agent,clearcontainers/agent