Issue was caused when exec is tarted, exits, then stated again.
In this case, `Close` is called twice, which closes a channel twice.
Changes execConfig.ExitCode to a pointer so we can test if the it has
been set or not.
This allows us to return early when the exec has already been run.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: 1a60a805bfabee729dbc833515cd0be439adb95b
Component: engine