report: gracefully handle XML report creation when no tests are run

If no tests are run (because they have all been excluded) then make
sure we insert a valid timestamp into the XML file, and avoid printing
an error message when reading a non-existent test summary scratch
file.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
1 file changed