This adds an additional interval to be used by healthchecks during the
start period.
Typically when a container is just starting you want to check if it is
ready more quickly than a typical healthcheck might run. Without this
users have to balance between running healthchecks to frequently vs
taking a very long time to mark a container as healthy for the first
time.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>