Update test-image-disk-simple integration test

Update slfo/test-image-disk-simple. Add more space for
flake testing and add a user to test flakes for non root

Author: schaefi

build-tests/x86/slfo/test-image-disk-simple/appliance.kiwi

@@ -19,10 +19,12 @@
                 <oem-resize>false</oem-resize>
             </oemconfig>
             <bootloader name="grub2" console="serial" timeout="10"/>
+            <size unit="G">4</size>
         </type>
     </preferences>
     <users>
         <user password="$1$wYJUgpM5$RXMMeASDc035eX.NbYWFl0" home="/root" name="root" groups="root"/>
+        <user password="$1$wYJUgpM5$RXMMeASDc035eX.NbYWFl0" home="/home/ec2-user" name="ec2-user" groups="users,root"/>
     </users>
     <repository type="rpm-md">
         <source path="obsrepositories:/"/>