Don't try to connect to nginx on client creation (#504)

The client now is created without making a call to nginx.
When Collect() is called we try to get the metrics from nginx and if
it's not available it will set 'up' to 0 and not fail anymore.

exporter_test.go

@@ -1,91 +1,11 @@
 package main
 
 import (
-	"errors"
 	"reflect"
 	"testing"
 	"time"
-
-	"github.com/go-kit/log"
 )
 
-func TestCreateClientWithRetries(t *testing.T) {
-	t.Parallel()
-
-	type args struct {
-		client        interface{}
-		err           error
-		retries       uint
-		retryInterval time.Duration
-	}
-
-	tests := []struct {
-		name            string
-		args            args
-		expectedRetries int
-		want            interface{}
-		wantErr         bool
-	}{
-		{
-			name: "getClient returns a valid client",
-			args: args{
-				client: "client",
-				err:    nil,
-			},
-			expectedRetries: 0,
-			want:            "client",
-			wantErr:         false,
-		},
-		{
-			name: "getClient returns an error after no retries",
-			args: args{
-				client: nil,
-				err:    errors.New("error"),
-			},
-			expectedRetries: 0,
-			want:            nil,
-			wantErr:         true,
-		},
-		{
-			name: "getClient returns an error after retries",
-			args: args{
-				client:        nil,
-				err:           errors.New("error"),
-				retries:       3,
-				retryInterval: time.Millisecond * 1,
-			},
-			expectedRetries: 3,
-			want:            nil,
-			wantErr:         true,
-		},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			invocations := 0
-			getClient := func() (interface{}, error) {
-				invocations++
-				return tt.args.client, tt.args.err
-			}
-
-			got, err := createClientWithRetries(getClient, tt.args.retries, tt.args.retryInterval, log.NewNopLogger())
-
-			actualRetries := invocations - 1
-
-			if actualRetries != tt.expectedRetries {
-				t.Errorf("createClientWithRetries() got %v retries, expected %v", actualRetries, tt.expectedRetries)
-				return
-			} else if (err != nil) != tt.wantErr {
-				t.Errorf("createClientWithRetries() error = %v, wantErr %v", err, tt.wantErr)
-				return
-			} else if err != nil && tt.wantErr {
-				return
-			} else if !reflect.DeepEqual(got, tt.want) {
-				t.Errorf("createClientWithRetries() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}
-
 func TestParsePositiveDuration(t *testing.T) {
 	t.Parallel()