library: exit on user creation failure

library: exit on user creation failure

When the ceph dashboard user creation fails then the issue is hidden
as we don't check the return code and don't print the error message
in the module output.

This ends up with a failure on the ceph dashboard set roles command saying
that the user doesn't exist.

By failing on the user creation, we will have an explicit explaination of
the issue (like weak password).

Closes: #6197
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 17784624e0fb02080e14d15b4105ef92a78ec8c4)