util: buffer: Simplify handling of indent overflows

util: buffer: Simplify handling of indent overflows

Rather than setting usage error truncate the indentation level. Having
the output string misformated is way more useful to figure out where the
error lies rather than reporting an error after a giant formatter
function.

In testBufAutoIndent we now validate that the indentation is truncated
and testBufAddBuffer2 is removed since it became bogus.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>