tests/libtest: follow our code style guidelines better

tests/libtest/chkhostname.c

tests/libtest/lib1500.c

tests/libtest/lib1501.c

tests/libtest/lib1506.c

tests/libtest/lib1507.c

tests/libtest/lib1510.c

tests/libtest/lib1512.c

tests/libtest/lib1515.c

tests/libtest/lib1525.c

tests/libtest/lib1526.c

tests/libtest/lib1527.c

tests/libtest/lib1528.c

tests/libtest/lib1531.c

tests/libtest/lib1900.c

tests/libtest/lib500.c

tests/libtest/lib501.c

tests/libtest/lib504.c

tests/libtest/lib505.c

tests/libtest/lib506.c

tests/libtest/lib508.c