Allow system_server to set ctl.bugreport property.

Resolves denials such as:
avc:  denied  { set } for property=ctl.bugreport scontext=u:r:system_server:s0 tcontext=u:object_r:ctl_bugreport_prop:s0 tclass=property_service

Change-Id: I6c3085065157f418fc0cd4d01fa178eecfe334ad
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>