ipatests: fix ipahealthcheck fixture _modify_permission
    
    The test is storing the initial file permissions obtained with 'stat',
    then modifies them, calls ipa-healthcheck and reverts the permissions
    to the original value.
    
    When the file is a symlink, stat returns the permissions of the link,
    not of the pointed-to file. But chmod modifies the permissions of the
    pointed-to file, not of the link.
    As a consequence, the fixture does not properly restore the original
    file permissions.
    
    The fix consists in calling 'stat -L' because the command follows
    links.
    
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>