Vultr API is being inconsisten in what it returns. An empty list when no
resources exists, but a dict of dict when they do. The case needs to be
handled so the module do not fail. An extra test has been added.
This commit introduces a new module called vr_sshkey_facts.
This module aims to return the list of SSH keys avaiable in Vultr.
Sample available here:
```
"vultr_sshkey_facts": [
{
"date_created": "2018-07-10 14:49:13",
"id": "5b43c760d7d84",
"name": "me@home",
"ssh_key": "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC+ZFQv3MyjtL1BMpSA0o0gIkzLVVC711rthT29hBNeORdNowQ7FSvVWUdAbTq00U7Xzak1ANIYLJyn+0r7olsdG4XEiUR0dqgC99kbT/QhY5mLe5lpl7JUjW9ctn00hNmt+TswpatCKWPNwdeAJT2ERynZaqPobENgewrwerqewqIVew7qFeZygxsPVn36EUr2Cdq7Nb7U0XFXh3x1p0v0+MbL4tiJwPlMAGvFTKIMt+EaA+AsRIxiOo9CMk5ZuOl9pT8h5vNuEOcvS0qx4v44EAD2VOsCVCcrPNMcpuSzZP8dRTGU9wRREAWXngD0Zq9YJMH38VTxHiskoBw1NnPz me@home"
}
]
```
