fix broken unit tests by avoid triggering deprecated behaviour (unless intended)

this also includes the fixes in #1123, #1124 and #1127 which are required to make all tests pass
`init_config` reinitialises the active EasyBuild configuration, it needs to be (re)called whenever you change something that affects the configuration (like fiddling with the deprecation version)

it's only relevant for tests which may rely on EB being configured in a certain way