Use custom default branch in protected branches

And maven YAML config
Signed-off-by: Nailia Iskhakova <niskhakova@gitlab.com>

qa/qa/resource/protected_branch.rb

@@ -22,7 +22,7 @@ module QA
         Resource::Repository::Commit.fabricate_via_api! do |commit|
           commit.project = project
           commit.branch = branch_name
-          commit.start_branch = 'master'
+          commit.start_branch = project.default_branch
           commit.commit_message = 'Add new file'
           commit.add_files([
             { file_path: "new_file-#{SecureRandom.hex(8)}.md", content: 'new file' }

qa/qa/specs/features/browser_ui/5_package/maven_repository_spec.rb

@@ -132,7 +132,7 @@ module QA
                       - 'mvn deploy -s settings.xml'
                       - "mvn dependency:get -Dartifact=#{group_id}:#{artifact_id}:1.0"
                     only:
-                      - master
+                      - "#{project.default_branch}"
                     tags:
                       - "runner-for-#{project.name}"
                 YAML