trivial: Load the plugins from disk in a predicatable way

This allows us to compare the verbose output using GS_DEBUG_NO_TIME=1
1 job for <span class="ref-name">wip/hughsie/filesystem-random-ordering</span> in 8 minutes and 30 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #66192
build-gnome-software

00:08:30