Do not automatically remove tmp/sources directory with epoch changes

This commit adds changes to not remove tmp/sources directory automatically when epoch changes but instead raise an exception. In case an env variable is set, system will then force the removal of these directories otherwise they would have to be done manually.

scale_build/config.py

@@ -9,6 +9,7 @@ BUILD_TIME_OBJ = datetime.fromtimestamp(BUILD_TIME)
 BUILDER_DIR = os.getenv('BUILDER_DIR', './')
 BRANCH_OUT_NAME = os.getenv('NEW_BRANCH_NAME')
 BRANCH_OVERRIDES = {k[:-(len('_OVERRIDE'))]: v for k, v in os.environ.items() if k.endswith('_OVERRIDE')}
+FORCE_CLEANUP_WITH_EPOCH_CHANGE = os.getenv('FORCE_CLEANUP_WITH_EPOCH_CHANGE', False)
 GITHUB_TOKEN = os.getenv('GITHUB_TOKEN')
 PARALLEL_BUILD = int(os.getenv('PARALLEL_BUILDS', max(os.cpu_count(), 8) / 4))
 PKG_DEBUG = os.getenv('PKG_DEBUG', False)