TMT: adjust ROOTLESS_USER env var on ELN

The default rootless user is set to `cloud-user` on both RHEL and ELN
environments, while it's `ec2-user` on CentOS Stream and `fedora` on
Fedora.

Signed-off-by: Lokesh Mandvekar <[email protected]>

Author: lsm5

test/main.fmf

@@ -29,6 +29,6 @@ recommend:
         - when: distro == centos-stream
           environment+:
             ROOTLESS_USER: "ec2-user"
-        - when: distro == rhel
+        - when: distro == fedora-eln or distro == rhel
           environment+:
             ROOTLESS_USER: "cloud-user"