grant webviewupdate_service app_api_service attribute

avc:  denied  { find } for service=webviewupdate pid=11399 uid=10070 scontext=u:r:untrusted_app:s0:c512,c768 tcontext=u:object_r:webviewupdate_service:s0 tclass=service_manager permissive=0

Bug: 25018574
Change-Id: I26a7846d1c80c1ab3842813f4148528030b1106a