Configures tests to use their own file depot folder

tracim/test.ini

 port = 8080
 
 [app:main]
+depot_storage_dir = /tmp/tracim_tests_depot/
 # sqlalchemy.url = postgresql://tracimuser:tracimpassword@127.0.0.1:5432/tracimdb_test?client_encoding=utf8
 # sqlalchemy.url = mysql+pymysql://tracimuser:tracimpassword@127.0.0.1/tracimdb_test
 sqlalchemy.url = sqlite:///tracimdb_test.sqlite