Fixed cancel block storage issue

[FernandoOjeda]

Cancel block storage issue #880

[coveralls]

Coverage increased (+0.003%) to 88.142% when pulling 64fe8b0 on FernandoOjeda:fo_cancel_block_storage into 32a6e43 on softlayer:master.

[allmightyspiff]

To get the tox -e analysis check to pass, heres how you handle the following complaints.

C:515, 0: Unnecessary parens after 'print' keyword (superfluous-parens)
Should be removed once you switch from print to throw exception

C:513, 8: Variable name "billingItem" doesn't conform to snake_case naming style (invalid-name)

change billingItem to billing_item

R:501, 4: Either all return statements in a function should return an expression, or none of them should. (inconsistent-return-statements)
Removing the else: block should fix this.

Also, please add a unit test for this new if condition so test coverage doesn't go down.

Thanks :)

[allmightyspiff]

The managers should not print out anything. I'd rather we raise an exception here.
https://github.com/softlayer/softlayer-python/blob/master/SoftLayer/managers/hardware.py#L87 has a good example of how to handle this sort of logic.

[allmightyspiff]

Since were going to throw an exception if we don't have a billing item, the else bits are not really needed and can be reverted back.