MM-19790: Remove randomness in oauth test AuthData. (#12988)

The ID field of Gitlab OAuth data was generated as a random number
between 1-1000. Unfortunately, this gave a 1 in 1 million chance of two
users generated this way colliding and meaning if you had two test users
in a test case they silently ended up actually being the exact same
user. We don't actually need to generate this randomly, so instead
change to having the test cases explicitly set the ID number so the
behaviour is as expected and completely deterministic.

As you'd expect, with odds of exactly a million to 1, it just might
(and in this case, it did indeed) happen.

app/user_test.go

@@ -8,7 +8,6 @@ import (
 	"encoding/json"
 	"image"
 	"image/color"
-	"math/rand"
 	"strings"
 	"testing"
 	"time"
@@ -74,8 +73,7 @@ func TestCreateOAuthUser(t *testing.T) {
 	th := Setup(t).InitBasic()
 	defer th.TearDown()
 
-	r := rand.New(rand.NewSource(time.Now().UnixNano()))
-	glUser := oauthgitlab.GitLabUser{Id: int64(r.Intn(1000)) + 1, Username: "o" + model.NewId(), Email: model.NewId() + "@simulator.amazonses.com", Name: "Joram Wilander"}
+	glUser := oauthgitlab.GitLabUser{Id: 42, Username: "o" + model.NewId(), Email: model.NewId() + "@simulator.amazonses.com", Name: "Joram Wilander"}
 
 	json := glUser.ToJson()
 	user, err := th.App.CreateOAuthUser(model.USER_AUTH_SERVICE_GITLAB, strings.NewReader(json), th.BasicTeam.Id)
@@ -253,8 +251,8 @@ func TestUpdateOAuthUserAttrs(t *testing.T) {
 
 	var user, user2 *model.User
 	var gitlabUserObj oauthgitlab.GitLabUser
-	user, gitlabUserObj = createGitlabUser(t, th.App, username, email)
-	user2, _ = createGitlabUser(t, th.App, username2, email2)
+	user, gitlabUserObj = createGitlabUser(t, th.App, 1, username, email)
+	user2, _ = createGitlabUser(t, th.App, 2, username2, email2)
 
 	t.Run("UpdateUsername", func(t *testing.T) {
 		t.Run("NoExistingUserWithSameUsername", func(t *testing.T) {
@@ -443,9 +441,8 @@ func getGitlabUserPayload(gitlabUser oauthgitlab.GitLabUser, t *testing.T) []byt
 	return payload
 }
 
-func createGitlabUser(t *testing.T, a *App, username string, email string) (*model.User, oauthgitlab.GitLabUser) {
-	r := rand.New(rand.NewSource(time.Now().UnixNano()))
-	gitlabUserObj := oauthgitlab.GitLabUser{Id: int64(r.Intn(1000)) + 1, Username: username, Login: "user1", Email: email, Name: "Test User"}
+func createGitlabUser(t *testing.T, a *App, id int64, username string, email string) (*model.User, oauthgitlab.GitLabUser) {
+	gitlabUserObj := oauthgitlab.GitLabUser{Id: id, Username: username, Login: "user1", Email: email, Name: "Test User"}
 	gitlabUser := getGitlabUserPayload(gitlabUserObj, t)
 
 	var user *model.User