Description of problem:
GCE credentials (service account data) is saved into json file. We should add an option to upload this file. Currently only copy (from json file) paste (into text input) is available. 

Version-Release number of selected component (if applicable):
5.6.0.7

How reproducible:
Always

Steps to Reproduce:
1) Go to Compute -> Cloud -> Providers 
1) Press Configuration -> Add a New Cloud Provider
2) Choose type Google Compute Engine
3)

Actual results:
Unable to upload the service account json file.

Expected results:
A file upload input option should be available

Additional info:
The json file contains a lot of information and private key what make impossible to read, correct or enter manually any data in "Service Account JSON" input. Only copy & paste is an option.