Pull request: clear working directory after each build to prevent agent's disk bloat

Merge in DNS/adguard-home from clean-working-directory to master

Squashed commit of the following:

commit cf5908c8bff984544f6d6fcad5bcd0b8e2109225
Author: Константин Замякин <sc@adguard.com>
Date:   Wed Apr 14 02:06:20 2021 +0300

    clear working directory after each build to prevent agent's disk bloat

bamboo-specs/test.yaml

@@ -22,6 +22,8 @@
       '${system.GO_CACHE_DIR}': '${bamboo.cacheGo}'
       '${system.GO_PKG_CACHE_DIR}': '${bamboo.cacheGoPkg}'
   'key': 'TEST'
+  'other':
+    'clean-working-dir': true
   'tasks':
   - 'checkout':
       'force-clean-build': true