examples.wrappers: Use exec and "$@" in valgrind.sh.

Use "$@" for command line execution.

Signed-off-by: Rudá Moura <rmoura@redhat.com>
examples.wrappers: New wrapper time.sh.

New wrapper script: run process inside /usr/bin/time.

Signed-off-by: Rudá Moura <rmoura@redhat.com>