fix IrodsConnection disconnect()

refactoring left a mistake
fix the irodsstorage read() signature

add the "query" parameter that gets passed. before, it was
erroneously assigned to "conn", which led to double assignment
in the generator @get_connection()
fix the read() default parameters

change the parameter default range_list=[] to None to avoid
that this default is changed through subsequent calls.
This affects all storage implementations.