Misc typos in nova

1. on demands -> on demand
2. Either Network -> Either network
3. unexpected task -> Unexpected task
4. PCI Device -> PCI device
5. key manager -> Key manager

Change-Id: I5a3cb64b38e8851902492c15fda7f63c4fa4f7f0
Closes-Bug: #1255914
Merge "Misc typos in nova"