tests: add spread suite for autotools plugin

[kyrofa]

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This PR resolves LP: #1783825 by moving the plugins and snapd tests for the Autotools plugin into a single Spread suite.

[codecov-io]

Codecov Report

Merging #2182 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2182      +/-   ##
==========================================
- Coverage   91.25%   91.23%   -0.02%     
==========================================
  Files         202      202              
  Lines       12861    12861              
  Branches     1907     1907              
==========================================
- Hits        11736    11734       -2     
- Misses        765      766       +1     
- Partials      360      361       +1

Impacted Files	Coverage Δ
snapcraft/internal/pluginhandler/_plugin_loader.py	91.96% <0%> (-1.79%)	⬇️

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