gdb: Fix printout of runtime

Fix the printout of runtime by "osv info threads" and "osv runqueue"
debugger commands, to fit the new scheduler (different variable name,
and it is float, not integer).

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>