omb_main: set nextboot after omb_utils_load_modules

We need to select the nextboot after omb_utils_load_modules because
nextboot might have different kernel.

Setting nextboot before omb_utils_load_modules we were trying to load
the modules of nextboot instead of (previously) selected kernel.
Merge pull request #11 from athoik/fix-nextboot

omb_main: set nextboot after omb_utils_load_modules