Improve test targets in Makefile
Improve test targets in Makefile

- enable running eunit and retest tests separately
- add neccessary dependencies to each test target so that
  one can just do 'make test' without recompiling changed files
  manually
- enable overwriting retest's log level
- use retest's own Makefile instead of invoking rebar manually

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