Hardware cancel consolidation

[sudorandom]

This should resolve #522.

• HardwareManager.cancel_metal() is removed in favor of HardwareManager.cancel_hardware()
• HardwareManager.cancel_hardware() now uses SoftLayer_Billing_Item::cancelItem() which (I think) works on most cancelable items.

[landscape-bot]

Code quality remained the same when pulling 769d900 on sudorandom:hardware-cancel into 200787d on softlayer:master.

[coveralls]

Coverage decreased (-0.02%) to 85.61% when pulling 769d900 on sudorandom:hardware-cancel into 200787d on softlayer:master.

[landscape-bot]

Code quality remained the same when pulling ab50844 on sudorandom:hardware-cancel into 200787d on softlayer:master.

[coveralls]

Coverage decreased (-0.02%) to 85.61% when pulling ab50844 on sudorandom:hardware-cancel into 200787d on softlayer:master.

[sudorandom]

@underscorephil Do you know if SoftLayer_Billing_Item::cancelItem() is the method to use that can cancel most things? I know they did a lot of work to consolidate cancellation but it's not obvious in the documentation which one should be used.

[underscorephil]

@sudorandom doing some research to make sure my info is up to date. Will keep you in the loop

[sudorandom]

@underscorephil so it looks like SoftLayer_Billing_Item::cancelItem is the universal cancel method. That will likely simplify a lot. I think this change is ready.

[underscorephil]

LGTM