use "graceful" instead of "reload" for Apache

The "reload" command is actually HUP which interrupts worker processes
in the middle of serving requests, whereas we actually want "graceful"
(USR1) which allows outstanding requests to finish.

http://httpd.apache.org/docs/2.2/stopping.html

Change-Id: I9fd6cfcffc06830a8c98289b6ba78fe603aae481