core.app: fix bug in compute_breathe_order...
core.app: fix bug in compute_breathe_order...

...for nodes without push.

Do collect valid push specs for all apps in the graph for use in
breathe order computation.
Only insert apps that have push() methods in
final breathe_push_order array.

eugeneia/snabb,eugeneia/snabb,eugeneia/snabb,eugeneia/snabb,eugeneia/snabb,eugeneia/snabb,snabbco/snabb,snabbco/snabb,snabbco/snabb,snabbco/snabb,eugeneia/snabb,snabbco/snabb,snabbco/snabb,eugeneia/snabb,snabbco/snabb,snabbco/snabb