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
Merge commit 'd9260dc1636aac510f3d34a01973e27cab5d9f79'