init: log Service failures via Result<T>

Log Service failures via Result<T> such that their context can be
captured when interacting with services through builtin functions.

Test: boot bullhead
Change-Id: I4d99744d64008d4a06a404e3c9817182c6e177bc
diff --git a/init/service.h b/init/service.h
index be173cd..1f2c44f 100644
--- a/init/service.h
+++ b/init/service.h
@@ -70,10 +70,10 @@
 
     bool IsRunning() { return (flags_ & SVC_RUNNING) != 0; }
     Result<Success> ParseLine(const std::vector<std::string>& args);
-    bool ExecStart();
-    bool Start();
-    bool StartIfNotDisabled();
-    bool Enable();
+    Result<Success> ExecStart();
+    Result<Success> Start();
+    Result<Success> StartIfNotDisabled();
+    Result<Success> Enable();
     void Reset();
     void Stop();
     void Terminate();