Keypairs endpoint extension for OpenStack compatibility

[kpelelis]

Implemented 4 endpoints that are part of the OpenStack Compute API in order to have CRUD operations on SSH keypairs. Most of the logic is implemented on

snf-cyclades-app/synnefo/api/keypairs.py

TODO: Decouple the models manipulation (create, update) from the API view

[skalkoto]

Hello, Thank you very much for the pull request. We are really looking forward to merge your patches, but first of all there are some issues with process that need to be addressed:

• Your commit messages have a wrong author
• You have 2 commits with the same message
• You have 2 commits (e7a46a9a0c6dca5c947b0b1c2793cf9142f4a40f and 168aa97bdd96168e1a889143a0670944bcd87736) which are almost identical. You can do git -i rebase ac7cab3332e to start an interactive rebase and squash those commits into 1.
• You have a merge commit in your pull request. This is not necessary. You need to rebase your branch to avoid it.
• Your commits are build over an old synnefo commit. We can fix this when merging but better do a rebase by yourself.

Some comment about small issues in the code will follow later on today.