tests/nested/manual/core20-remodel: wait for device to have a serial before starting a remodel

[bboozzoo]

Devices are expected to have serials before remodel can be started. We already have the right checks for tests/core, but not for nested tests.

[codecov-commenter]

Codecov Report

Merging #11131 (116fa26) into master (47873f2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #11131   +/-   ##
=======================================
  Coverage   78.23%   78.23%           
=======================================
  Files         917      917           
  Lines      103960   103960           
=======================================
  Hits        81333    81333           
+ Misses      17531    17530    -1     
- Partials     5096     5097    +1     

Flag	Coverage Δ
unittests	78.23% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
store/cache.go	69.23% <0.00%> (-1.93%)	⬇️
cmd/snap/cmd_debug_state.go	70.18% <0.00%> (-0.46%)	⬇️
overlord/snapstate/snapstate.go	82.88% <0.00%> (-0.13%)	⬇️
overlord/ifacestate/helpers.go	77.45% <0.00%> (+0.48%)	⬆️
daemon/api_connections.go	93.58% <0.00%> (+0.53%)	⬆️
interfaces/sorting.go	100.00% <0.00%> (+1.78%)	⬆️

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[stolowski]

LGTM

[mardy]

LGTM, though I wonder if there's some reason why you are not simply using the retry command.

[bboozzoo]

@mvo5 this is ready to land, can you merge?