This patch adds a 'restart_method' parameter to Launcher. When set to
'reload' (the default), behavior is as today. If a service chooses
'mutate' then when a SIGHUP is received, mutate_config_files is called
instead of reload_config_files. This means the 'mutable' flag on
options will be respected.
Change-Id: Icec3e664f3fe72614e373b2938e8dee53cf8bc5e
Depends-On: I9bb2ff39dc1ed0a63bd7e7635704b34c53d32d79