Improve reliability of test_read with reset before running

[sturmianseq]

This PR aims to improve the reliability of the test test_read by resetting the state before running the test.

The test may fail in the following way if it starts running from a polluted state:

    def test_read(config_files):
>       assert read() == {
 ......
E       AssertionError: assert {'Virtual Mac...: '443', ...}} == {'Virtual Mac...: '443', ...}}
E         Omitting 2 identical items, use -vv to show
E         Differing items:
E         {'Vsphere Session': {'vcdriver_host': '', 'vcdriver_idle_timeout': '7200', 'vcdriver_password': 'myway', 'vcdriver_port
': '443', ...}} != {'Vsphere Session': {'vcdriver_host': '', 'vcdriver_idle_timeout': '7200', 'vcdriver_password': '', 'vcdriver_
port': '443', ...}}
E         Use -v to get the full diff