source creds retrieved dynamically by the script

so far we just cat them and source them in the functest part. It is better to keep all the creds related action in the fetch creds scripts

JIRA: FUNCTEST-42

Change-Id: I4c422237398baf13a1af73232a74bd36f82faca7
Signed-off-by: Morgan Richomme <morgan.richomme@orange.com>