v15 Bugfixes

[kaelemc]

1. Allow a topology using defaults: to load

This is valid, but didn't load before.. still TBD is resolving the nodeConfig properly

name: srsim1
topology:
  defaults:
    kind: nokia_srsim
    image: nokia_srsim:25.7.R1
    license: ../lics/srsim.txt
  
  nodes:
    R1:
    R2:
    R3:
    R4:
  
  links:
    - endpoints: [R1:e1-1-c1-1, R2:e1-1-c1-1]
    - endpoints: [R3:e1-1-c1-1, R4:e1-1-c1-1]
    - endpoints: [R2:e1-1-c2-1, R4:e1-1-c2-1]
    - endpoints: [R1:e1-1-c2-1, R3:e1-1-c2-1]

[kaelemc]

2. Fix the yaml flow settings, so that when you delete all nodes and links in the edtior, and add back new links/nodes. the yaml looks natural, and not the style with curly braces or square brackets (even though it is valid yaml)

[kaelemc]

Probably good to go.. wait a while for some other people to report something. or you can merge already.