opkg-utils: warn if update-alternatives finds priority conflict

opkg-utils: warn if update-alternatives finds priority conflict

If multiple providers for a utility have the same alternatives priority,
which one would be chosen is determined by which one is installed later.
Our alternatives system should be able to detect such problem and warn users
so that potential problems could be avoided.

Modify update-alternatives to warn users when detecting multiple providers
with the same priority.

[YOCTO #8314]

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>