Using more than one docstrig directive makes Avocado to use only the
first one. This patch makes the safeloader to handle multiple docstring
directives (i.e. `🥑 enable` and `🥑 tags=foo`).

Reference: https://trello.com/c/6FpySXuCSigned-off-by: NAmador Pahim <apahim@redhat.com>