[RFC] Validate SSH key format and size in the SSHKeyDeployment class

[Kami]

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[Kami]

This is slightly off topic, but one thing I would also eventually like to do is refactor the libcloud.utils.pubkey module.

I would add a new PublicKey class which would handle all the public key related methods which are currently exported by pubkey module

Advantages of this approach are:

• No need to copy and paste "if pycrypto available" stuff
• This class would know how to deal with different key types (rsa, ecdsa, dsa)

Anyway, that's more of a low priority refactoring.