Probe revamped to provide for a new WrappedError struct to wrap probes as error interface

This convenience was necessary to be used for golang library functions like io.Copy and io.Pipe
where we shouldn't be writing proxies and alternatives returning *probe.Error

This change also brings more changes across code base for clear separation regarding where an error
interface should be passed encapsulating *probe.Error and where it should be used as is.

pkg/server/rpc/auth.go

@@ -49,7 +49,7 @@ func getAuth(reply *AuthReply) *probe.Error {
 // Get auth keys
 func (s *AuthService) Get(r *http.Request, args *Args, reply *AuthReply) error {
 	if err := getAuth(reply); err != nil {
-		return err
+		return probe.NewWrappedError(err)
 	}
 	return nil
 }

pkg/server/rpc/donut.go

@@ -56,5 +56,8 @@ func setDonut(args *DonutArgs, reply *Reply) *probe.Error {
 
 // Set method
 func (s *DonutService) Set(r *http.Request, args *DonutArgs, reply *Reply) error {
-	return setDonut(args, reply)
+	if err := setDonut(args, reply); err != nil {
+		return probe.NewWrappedError(err)
+	}
+	return nil
 }

pkg/server/rpc/sysinfo.go

@@ -55,7 +55,7 @@ func setSysInfoReply(sis *SysInfoReply) *probe.Error {
 	var err error
 	sis.Hostname, err = os.Hostname()
 	if err != nil {
-		return probe.New(err)
+		return probe.NewError(err)
 	}
 	return nil
 }
@@ -70,7 +70,7 @@ func setMemStatsReply(sis *MemStatsReply) *probe.Error {
 // Get method
 func (s *SysInfoService) Get(r *http.Request, args *Args, reply *SysInfoReply) error {
 	if err := setSysInfoReply(reply); err != nil {
-		return err
+		return probe.NewWrappedError(err)
 	}
 	return nil
 }
@@ -78,7 +78,7 @@ func (s *SysInfoService) Get(r *http.Request, args *Args, reply *SysInfoReply) e
 // Get method
 func (s *MemStatsService) Get(r *http.Request, args *Args, reply *MemStatsReply) error {
 	if err := setMemStatsReply(reply); err != nil {
-		return err
+		return probe.NewWrappedError(err)
 	}
 	return nil
 }