The libcmd unit test creates files (more specifically, the fetcher cache) in
its home directory. In the single-user sandbox, this leads to the creation of
/homeless-shelter, since this is the default HOME and the root is writable.
Unfortunately, this conflicts with the assumption of the functional tests that
this directory does not exist. Use a different home directory to prevent these
test failures, and thus restore the ability to build inside the single-user
sandbox.
Fixes: https://git.lix.systems/lix-project/lix/issues/365
Change-Id: I4df8c53d043234b95a7c0ac45fc5ee89e8d46aff