Jenkinsfile: skip ppc64le and s390x by default on pull requests
Jenkinsfile: skip ppc64le and s390x by default on pull requests

This changes CI to skip these platforms by default. The ppc64le and s390x
machines are "pet machines", configuration may be outdated, and these
machines are known to be flaky.

Building and verifying packages for these platforms is being handed
over to the IBM team.

We can still run these platforms for specific pull requests by selecting
the checkboxes.

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

thaJeztah/docker,jameszhan/docker,trebonian/docker,docker/docker,thaJeztah/docker,bearstech/moby,nawawi/docker,jthelin/docker,kojiromike/docker,Ramzec/docker,flavio/docker,mahak/docker,jimjag/docker,cpuguy83/docker,jameszhan/docker,moby/moby,moby/moby,gnailuy/docker,kojiromike/docker,bearstech/moby,trebonian/docker,djs55/docker,nalind/docker,flavio/docker,konstruktoid/docker-upstream,Ramzec/docker,cpuguy83/docker,moul/docker,cpuguy83/docker,trebonian/docker,mahak/docker,konstruktoid/docker-upstream,kojiromike/docker,bearstech/moby,thaJeztah/docker,nawawi/docker,nalind/docker,moul/docker,Mokolea/docker,yosifkit/docker,konstruktoid/docker-upstream,jthelin/docker,jimjag/docker,paralin/docker,moby/moby,docker/docker,gnailuy/docker,yosifkit/docker,AkihiroSuda/docker,AkihiroSuda/docker,djs55/docker,AkihiroSuda/docker,vdemeester/docker,cpuguy83/docker,nawawi/docker,flavio/docker,paralin/docker,yosifkit/docker,jimjag/docker,moul/docker,flavio/docker,vdemeester/docker,docker/docker,Ramzec/docker,Mokolea/docker,bearstech/moby,thaJeztah/docker,jameszhan/docker,Mokolea/docker,mahak/docker,paralin/docker,nalind/docker,paralin/docker,jimjag/docker,mahak/docker,gnailuy/docker,yosifkit/docker,nalind/docker,moby/moby,konstruktoid/docker-upstream,AkihiroSuda/docker,trebonian/docker,moul/docker,Ramzec/docker,vdemeester/docker,nawawi/docker,gnailuy/docker,djs55/docker,Mokolea/docker