New cloud provider CloudStack (#1420)

* clean commits from branch cloud-cloudstack w/ proper committer email/name

* fixed ansible-lint errors

* corrected typo in prompted message

* standalone cloudstack zones module

* added missing environment variables

* remove `_cloudstack_zones` default variable

* Move to Ubuntu 19.04

* Update cloud-cloudstack.md

* Update cloud-cloudstack.md

Markdown doesn't render `<your account>`

* Update prompts.yml

* Update main.yml

docs/cloud-cloudstack.md

@@ -0,0 +1,20 @@
+### Configuration file
+
+You need to create a configuration file in INI format with your api key in `$HOME/.cloudstack.ini`
+
+```
+[cloudstack]
+endpoint = <endpoint>
+key = <your api key>
+secret = <your secret>
+timeout = 30
+```
+
+Example for Exoscale (European cloud provider exposing CloudStack API), visit https://portal.exoscale.com/u/<your@account>/account/profile/api to gather the required information:  
+```
+[exoscale]
+endpoint = https://api.exoscale.com/compute
+key = <your api key>
+secret = <your secret>
+timeout = 30
+```