Corrections to Server createJson() for using keypairs with Rackspace

In lib/OpenCloud/Compute/Resource/Server.php the keypair['publicKey'] check (line 641) was incorrectly failing. Keys returned by compute->listKeypairs() do not have a "publicKey" element, but rather "public_key". Correction on line 644 is just to make the print function output match reality as well.

Lines 647-650 incorrectly cause createJson() to add a "keypair" array to the "server" json payload that is sent to nova API to create a server. At least in Rackspace's deployment, this leads to a server being created but no key being placed on the new instance. Example (incorrect at least at Rackspace) json payload made by function as-is:

{"server":{"name":"jamesl1","imageRef":"857d7d36-34f3-409f-8435-693e8797be8b","flavorRef":"2","metadata":{"sdk":"OpenCloud\/1.7.0 cURL\/7.34.0 PHP\/5.5.7-pl0-gentoo"},"networks":[{"uuid":"00000000-0000-0000-0000-000000000000"},{"uuid":"11111111-1111-1111-1111-111111111111"}],"keypair":{"key_name":"jamesl"}}}

The updated line 647 correctly adds "key_name" as a direct element of "server", causing createJson() to make a json payload that is both accepted by Rackspace's nova API and results in the key being placed on the instance. Example (correct at least at Rackspace) json payload made by modified line:

{"server":{"name":"jamesl1","imageRef":"857d7d36-34f3-409f-8435-693e8797be8b","flavorRef":"2","metadata":{"sdk":"OpenCloud\/1.7.0 cURL\/7.34.0 PHP\/5.5.7-pl0-gentoo"},"networks":[{"uuid":"00000000-0000-0000-0000-000000000000"},{"uuid":"11111111-1111-1111-1111-111111111111"}],"key_name":"jamesl"}}

When performing the unit tests, I found that tests/OpenCloud/Tests/Compute/Resource/ServerTest.php  also needed to be updated. It also had "publicKey" rather than "public_key" as the keypair key's attribute name. Corrected that and unit tests pass.

Changes to lib/OpenCloud/Common/Collection/PaginatedIterator.php  that are included by github in this pull request were not from me.