Consider to change the test suite, since nose will not likely work in the future

[Iximiel]

@gtribello, by reading the manual of nose I found that the first sentence is:

Nose has been in maintenance mode for the past several years and will likely cease without a new person/team to take over maintainership. New projects should consider using Nose2, py.test, or just plain unittest/unittest2.

That is not fun to read.

I found that nose do not work on python >=3.10, and since python 3.8, used in the test/compile suit, is EOL and 3.9 is going to cease support next year, I think PlumedToHTML should move to something else for the test suite
It should not be painful since the tests are plain unittests and nose is only used to run and postprocess them