fix lint warnings (issue 2541) (#2551)

* Lint: fix some errcheck #2541

* Lint: fix passing structcheck #2541

* Lint: update fix structcheck #2541

* Lint: fix errcheck for basicauth, browse, fastcgi_test #2541

* Lint: fix errcheck for browse, fastcgi_test, fcgiclient, fcgiclient_test #2541

* Lint: fix errcheck for responsefilter_test, fcgilient_test #2541

* Lint: fix errcheck for header_test #2541

* Lint: update errcheck for fcgiclient_test #2541

* Lint: fix errcheck for server, header_test, fastcgi_test, https_test, recorder_test #2541

* Lint: fix errcheck for tplcontext, vhosttrie_test, internal_test, handler_test #2541

* Lint: fix errcheck for log_test, markdown mholt#2541

* Lint: fix errcheck for policy, body_test, proxy_test #2541

* Lint: fix errcheck for on multiple packages #2541

- reverseproxy
- reverseproxy_test
- upstream
- upstream_test
- body_test

* Lint: fix errcheck in multiple packages mholt#2541
- handler_test
- redirect_test
- requestid_test
- rewrite_test
- fileserver_test

* Lint: fix errcheck in multiple packages mholt#2541

- websocket
- setup
- collection
- redirect_test
- templates_test

* Lint: fix errcheck in logger test #2541

run goimports against #2551
- lexer_test
- log_test
- markdown

* Update caddyhttp/httpserver/logger_test.go

Co-Authored-By: Inconnu08 <taufiqrx8@gmail.com>

* Update log_test.go

* Lint: fix scope in logger_test #2541

* remove redundant err check in logger_test #2541

* fix alias in logger_test #2541

* fix import for format #2541

* refactor variable names and error check #2541

caddyhttp/httpserver/vhosttrie_test.go

@@ -15,6 +15,7 @@
 package httpserver
 
 import (
+	"log"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -103,7 +104,9 @@ func populateTestTrie(trie *vhostTrie, keys []string) {
 		func(key string) {
 			site := &SiteConfig{
 				middlewareChain: HandlerFunc(func(w http.ResponseWriter, r *http.Request) (int, error) {
-					w.Write([]byte(key))
+					if _, err := w.Write([]byte(key)); err != nil {
+						log.Println("[ERROR] failed to write bytes: ", err)
+					}
 					return 0, nil
 				}),
 			}
@@ -139,7 +142,9 @@ func assertTestTrie(t *testing.T, trie *vhostTrie, tests []vhostTrieTest, hasWil
 
 		// And it must be the correct value
 		resp := httptest.NewRecorder()
-		site.middlewareChain.ServeHTTP(resp, nil)
+		if _, err := site.middlewareChain.ServeHTTP(resp, nil); err != nil {
+			log.Println("[ERROR] failed to serve HTTP: ", err)
+		}
 		actualHandlerKey := resp.Body.String()
 		if actualHandlerKey != test.expectedKey {
 			t.Errorf("Test %d: Expected match '%s' but matched '%s'",