tests: set branch name when initializing git repositories

prevent these warnings to pollute the output:

hint: Using 'master' as the name for the initial branch. This default branch name
hint: is subject to change. To configure the initial branch name to use in all
hint: of your new repositories, which will suppress this warning, call:
hint:
hint: 	git config --global init.defaultBranch <name>
hint:
hint: Names commonly chosen instead of 'master' are 'main', 'trunk' and
hint: 'development'. The just-created branch can be renamed via this command:
hint:
hint: 	git branch -m <name>

slapos/recipe/build/tests.py

@@ -152,7 +152,7 @@ class GitCloneNonInformativeTests(TestCase):
     os.mkdir(self.project_dir)
 
     # Add files and folder in parent repo and initialize git in it
-    check_call(['git', 'init'], cwd=self.project_dir)
+    check_call(['git', 'init', '--initial-branch', 'main'], cwd=self.project_dir)
     self.setUpGitConfig(self.project_dir)
     os.mkdir(os.path.join(self.project_dir, 'dir1'))
     self.touch(self.project_dir, 'file1.py')
@@ -169,7 +169,7 @@ class GitCloneNonInformativeTests(TestCase):
     os.mkdir(self.submodule_dir)
 
     # Add files in submodule repo and initialize git in it
-    check_call(['git', 'init'], cwd=self.submodule_dir)
+    check_call(['git', 'init', '--initial-branch', 'main'], cwd=self.submodule_dir)
     self.setUpGitConfig(self.submodule_dir)
     self.touch(self.submodule_dir, 'file1.py')
     self.gitAdd(self.submodule_dir)
@@ -356,7 +356,7 @@ repository = %s
     # pointer on parent repo and commit it
     submodule_dir_main_repo = os.path.join(self.project_dir, 'dir1',
                                            'submodule_repo')
-    check_call(['git', 'checkout', 'master'], cwd=submodule_dir_main_repo)
+    check_call(['git', 'checkout', 'main'], cwd=submodule_dir_main_repo)
     check_call(['git', 'pull', '--ff'], cwd=submodule_dir_main_repo)
     self.gitAdd(self.project_dir)
     self.gitCommit(self.project_dir, msg='Update submodule version')