Fix travis-ci tests
Fix travis-ci tests

Spinning up a distributed Erlang node by running 'erl -name ct3' failed
due to FQDN issues. Hiro Asari from Travis-CI suggested to try out the
new container-based workers as a fix, and that one works as expected
because we get a proper FQDN. Therefore, make the switch to
container-based workers.

rebar/rebar,dcarastan/rebar,CMoH/rebar,apache/couchdb-rebar,K2InformaticsGmbH/rebar,K2InformaticsGmbH/rebar,matwey/rebar,cloudant/couchdb-rebar,GabrielNicolasAvellaneda/rebar,choptastic/rebar,matwey/rebar,evnix/rebar,K2InformaticsGmbH/rebar,scatterbrain/rebar,bsmr-erlang/rebar,paulo-ferraz-oliveira/rebar,norton/rebar,jacktang/rebar,lrascao/rebar,choptastic/rebar,macintux/rebar,lrascao/rebar,oubiwann/rebar,scatterbrain/rebar,RubberCthulhu/rebar,lrascao/rebar,rebar/rebar,matwey/rebar,oubiwann/rebar,beni55/rebar,csyangchen/rebar,csyangchen/rebar,dcarastan/rebar,csyangchen/rebar,cloudant/couchdb-rebar,macintux/rebar,jacktang/rebar,CMoH/rebar,RubberCthulhu/rebar,GabrielNicolasAvellaneda/rebar,bsmr-erlang/rebar,lrascao/rebar,bsmr-erlang/rebar,GabrielNicolasAvellaneda/rebar,platinumthinker/rebar,oubiwann/rebar,paulo-ferraz-oliveira/rebar,norton/rebar,shkumagai/rebar,lrascao/rebar,norton/rebar,choptastic/rebar,bsmr-erlang/rebar,beni55/rebar,K2InformaticsGmbH/rebar,SiDen/rebar,SiDen/rebar,lpgauth/rebar,matwey/rebar,norton/rebar,dcarastan/rebar,shkumagai/rebar,lpgauth/rebar,shkumagai/rebar,beni55/rebar,evnix/rebar,rebar/rebar,apache/couchdb-rebar,cloudant/couchdb-rebar,lpgauth/rebar,apache/couchdb-rebar,evnix/rebar,SiDen/rebar,platinumthinker/rebar,jacktang/rebar,macintux/rebar,scatterbrain/rebar,matwey/rebar,CMoH/rebar,platinumthinker/rebar,paulo-ferraz-oliveira/rebar,K2InformaticsGmbH/rebar