tests: add spread suite for meson plugin

[kyrofa]

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This PR resolves LP: #1783837 by moving the plugin integration tests for the Meson plugin into a Spread suite.

[sergiusens]

meson is not available on trusty.

And I thought know how this creeped up again, but we had this issues before,
meson.build:2:0: ERROR: Target names starting with 'meson-' are reserved for Meson's internal use. Please rename.

[codecov-io]

Codecov Report

Merging #2205 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2205   +/-   ##
=======================================
  Coverage   91.18%   91.18%           
=======================================
  Files         202      202           
  Lines       12988    12988           
  Branches     1922     1922           
=======================================
  Hits        11843    11843           
  Misses        777      777           
  Partials      368      368

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[kyrofa]

meson is not available on trusty.

Ah very good. Fixed.

And I thought know how this creeped up again, but we had this issues before,
meson.build:2:0: ERROR: Target names starting with 'meson-' are reserved for Meson's internal use. Please rename.

My mistake, I've fixed it.