Bug 32939: Uniformize api calls

Bug 32939: Uniformize api calls

We want to make the call easier and without less errors possible.
Here, no need to async keyword, try-catch, etc.
Only call the method and use the common then with the 2 success and
error Promise arguments.

We will certainly want to add later a parameter to prevent the display
of the error in fetchJSON, in case the failure does not require a message
for the end user.

Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>