account for trailing exponent in test call_function's regexp

`call_function` started failing on my machine for no apparent reason.  I think this is because the `%g` format used by its `print_time` function is allowed to print an exponent, but the regular expression in `call_function.py` failed to account for that.  *Why* it started printing the exponent is unclear, but I did adjust the system time on my VM, so maybe that accounts for it...