fix test script to use "log" module

this adapts the test script to the changes to ImsXMLlib from
commit:af75d8279e3616208505acf649e23c0a9d01b61b
move parsing from useless function to __init__()
use string-check method from numpy
accept strings as well, not just filehandles

The etree.parse() call was already able to handle a str object instead of a
filehandle, just the logging call expected a string, this is fixed so the
ImarisXML object can now be created from both types.

The test script is adjusted accordingly to cover both cases.