Allow including @ and dot (.) characters in keypair name for OpenStack Compute (nova)

Keypair names currently only allow digits, ascii letters and "_- " But some users (a lot?) try to create their keypair including a '@' or '.' (dot) symbol in it, which is not allowed. This "convention" or habit might come from the default comment generated by ssh-keygen, which is user@host. Allowing the '@' and '....