tests: add tests for socket-util.c

add tests for:
- socket_address_is
- socket_address_is_netlink
- sockaddr_equal
tests: add missing unlink
tests: add tests for fileio.c

add tests for:
- write_string_stream
- write_string_file
- sendfile_full
tests: add test for fdset_iterate
tests: add tests for util.c

add tests for:
- is_symlink
- pid_is_unwaited
- pid_is_alive
- search_and_fopen
- search_and_fopen_nulstr
- glob_exists
- execute_directory
tests: add test-condition-util
tests: add tests for time-util.c

add tests for:
- timezone_is_valid
- get_timezones
tests: add missing entry to test-tables