git tests: setup default username for auxiliary repositories

Otherwise Git tries to get a username/email from the OS settings,
which sometimes fail on test server agents, and it leads to
commit failure.

plugins/git4idea/tests/git4idea/repo/GitWorkTreeBaseTest.kt

@@ -23,6 +23,7 @@ import git4idea.config.GitVersion
 import git4idea.test.GitPlatformTest
 import git4idea.test.git
 import git4idea.test.registerRepo
+import git4idea.test.setupDefaultUsername
 import org.junit.Assume.assumeTrue
 import java.io.File
 
@@ -44,6 +45,7 @@ abstract class GitWorkTreeBaseTest : GitPlatformTest() {
     val gitDir = LocalFileSystem.getInstance().refreshAndFindFileByIoFile(File(projectPath, GitUtil.DOT_GIT))
     assertNotNull(gitDir)
     myRepo = registerRepo(project, projectPath)
+    setupDefaultUsername()
     assertEquals(1, repositoryManager.repositories.size)
     assertNotNull(repositoryManager.getRepositoryForRoot(projectRoot))
   }

plugins/git4idea/tests/git4idea/test/GitTestUtil.kt

@@ -91,11 +91,12 @@ fun GitPlatformTest.cloneRepo(source: String, destination: String, bare: Boolean
   else {
     git("clone -- . $destination")
   }
+  cd(destination)
+  setupDefaultUsername()
 }
 
-fun setupDefaultUsername(project: Project) {
-  setupUsername(project, USER_NAME, USER_EMAIL)
-}
+fun setupDefaultUsername(project: Project) = setupUsername(project, USER_NAME, USER_EMAIL)
+fun GitPlatformTest.setupDefaultUsername() = setupDefaultUsername(project)
 
 fun setupUsername(project: Project, name: String, email: String) {
   assertFalse("Can not set empty user name ", name.isEmpty())

plugins/git4idea/tests/git4idea/update/GitSubmoduleTest.kt

@@ -169,7 +169,7 @@ class GitSubmoduleTest : GitPlatformTest() {
     git("init $moduleName")
     val child = File(testRoot, moduleName)
     cd(child)
-    setupDefaultUsername(project)
+    setupDefaultUsername()
     tac("initial.txt", "initial")
     val parent = "$moduleName.git"
     git("remote add origin ${testRoot}/$parent")
@@ -185,7 +185,10 @@ class GitSubmoduleTest : GitPlatformTest() {
   private fun prepareSecondClone(): File {
     cd(testRoot)
     git("clone --recurse-submodules parent.git bro")
-    return File(testRoot, "bro")
+    val broDir = File(testRoot, "bro")
+    cd(broDir)
+    setupDefaultUsername()
+    return broDir
   }
 
   private fun commitAndPushFromSecondClone(bro: File) {