Use common httpserver across fission (#2409)

* Defining httpserver package to capture httpserver shutdown and
introduces uniform running of http server across codebase.
* Add unit tests for httpserver

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/utils/httpserver/server.go

@@ -0,0 +1,32 @@
+package httpserver
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"go.uber.org/zap"
+)
+
+func StartServer(ctx context.Context, log *zap.Logger, svc string, port string, handler http.Handler) {
+	server := http.Server{
+		Addr:    fmt.Sprintf(":%s", port),
+		Handler: handler,
+	}
+	l := log.With(zap.String("service", svc), zap.String("addr", server.Addr))
+	l.Info("starting server")
+	go func() {
+		if err := server.ListenAndServe(); err != nil {
+			if err != http.ErrServerClosed {
+				l.Error("server error", zap.Error(err))
+			}
+		}
+	}()
+	<-ctx.Done()
+	l.Info("shutting down server")
+	if err := server.Shutdown(ctx); err != nil {
+		if err != context.Canceled && err != context.DeadlineExceeded {
+			l.Error("server shutdown error", zap.Error(err))
+		}
+	}
+}