ipatests: check if username are not optimized out in semanage context
    
    ipa users having default semanage context were optimized out.
    This test checks if those users are listed.
    
    related ticket : https://pagure.io/SSSD/sssd/issue/3819
    
    Signed-off-by: Mohammad Rizwan Yusuf <myusuf@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>