utils_cluster: fix dictionary-valueiterator issue

(discovered with unit tests, yay)

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
tests/utils_cluster: exercise cluster_pcs_flatiron predicate

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
commands/ccs2pcs: use cluster_pcs_flatiron instead in alias

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
utils_cluster: update knowledge about cluster in Fedora

+ also update the unit test(s)

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
utils_cluster: update knowledge about cluster in Ubuntu

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>