Write unit test for `Oracle module`

[ThanhNhann]

Currently, Oracle module is lacking some unit tests for functions so we need to handle them, below is the list of functions we need to do:

• func (k *Keeper) ProcessBandOraclePrices()
• func (k *Keeper) GetPrice()
• func (k *Keeper) RequestBandOraclePrices()
• func (k *Keeper) updateBandPriceStates()