tests: simplify formatting

tests: simplify formatting

The shell version would output 40 extra spaces for a test with
a multiple of 40 sub-tests, and the C version can use the same
printf optimization for avoiding a loop over single space output
as the shell version.

* tests/testutils.c (virtTestMain): Avoid loop for alignment.
* tests/test-lib.sh: Fix formatting when counter is multiple of 40.