I've been investigating about your question and it seems that disabling the USB Host it's not possible.
According to Kernel Power Management document (https://www.kernel.org/doc/Documentation/usb/power-management.txt) this is no longer possible. In Kernels up to 2.6.32, you could also specify "suspend", meaning that the device should remain suspended and autoresume was not allowed. Since Galileo uses a Kernel 3.8.7, this setting is not supported.
Thank you very much!