Fix a multitude of problems in set_scheme_manual.

When waiting for a wireless connection: loop until iwconfig shows us
actually connected.
Don't do wireless stuff for wired connections.
Catch the mysterious error where the /sys/class device file sometimes
isn't there (may related to switching between wired/wireless?)
Fix a few code factoring errors (modules not loaded).
Add a comment explaining that the misleading Connection class isn't used.