Initialize log before first use in cmd_proc()

`LOG_DEST` is used in `cmd_proc()`, but is initialized in `initialize_log()`, which therefore has to come first. In `vic_classic.c` this is simply a reversal of the function calls. Also added `initialize_log()` to `vic_image.c`. Without this a call to `vic_classic -o` or `vic_image -o` exits with a seg fault.