Do not assume env var QMTTEST_NAME will always be set

Currently a number of options assume the env var QMTTEST_NAME will be set.

This is true when those options are run inside a QMT test, but if a user runs by hand

gaudirun.py /path/to/test.qmt

this is not the case.

This MR checks if the env var is set, and if not defines a default name to use instead.