tests: Fix cleaning up after tests

Some of the test failed, because files (eg. mountpoint) were removed before
killing all the processes spawned by the tests. This commit makes the tests
kill all the processes first and then remove all the files.
cmake: Remove unused inline test

The test_inline.cc file was not used and had a common prefix
with the tests/ directory making it harder to use tab completion
when navigating through our sources.
chunkserver: Remove BGJOBS ifdefs

LizardFS doesn't support BGJOBS-less configurations anymore.
Remove preprocessor directives and code related to them.