understand log_directory and shared_part_list

These are options passed by test node, so that tests:
- can expose their logs while they are running ( see
  nexedi/erp5@34601253 )
- can use existing shared parts if they need to install
  software in a recursive slapos ( see
  nexedi/erp5@35768fa2 )

nxdtest

@@ -109,6 +109,8 @@ def main():
     parser.add_argument('--test_suite_title', help='The test suite title')
     parser.add_argument('--test_node_title', help='The test node title')
     parser.add_argument('--project_title', help='The project title')
+    parser.add_argument('--log_directory', help='Directory to store logs')
+    parser.add_argument('--shared_part_list', help='%s separated list of directories containing read only shared parts' % os.pathsep)
 
     parser.add_argument('--verbose', action='store_true', help='increase output verbosity')
 
@@ -156,6 +158,12 @@ def main():
     else:
         test_result = LocalTestResult(tenv, run=args.run)
 
+    # set conventional enironment variables
+    if args.log_directory:
+        os.environ['SLAPOS_TEST_LOG_DIRECTORY'] = args.log_directory
+    if args.shared_part_list:
+        os.environ['SLAPOS_TEST_SHARED_PART_LIST'] = args.shared_part_list
+
     # make sure we get output from subprocesses without delay.
     # go does not buffer stdout/stderr by default, but python does for stdout.
     # tell python not to buffer anything.