Concatenate global and agent plugins list
Concatenate global and agent plugins list

This part should have been added in the previous commit but I missed
it.

Related to T3222

SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site,SoftwareHeritage/puppet-swh-site