PR #70862 made each driver responsible for resetting its config, but
as it turned out, one place was missed in that PR: the in-tree gcepd
sets a node selector. Not resetting that caused other tests to fail
randomly depending on test execution order.
Now the test suite resets the config by taking a copy after setting up
the driver and restoring that copy before each test.
Long term the intention is to separate the entire test config from the
static driver info (https://github.com/kubernetes/kubernetes/issues/72288),
but for now resetting the config is the fastest way to fix the test flake.
Fixes: #72378
98ba1d8519