Use Ubuntu Precise for Travis unit test jobs (#4572)
Use Ubuntu Precise for Travis unit test jobs (#4572)

* Use Ubuntu Precise for Travis jobs

* Use trusty for Travis integration tests

nishantmonu51/druid,taochaoqiang/druid,druid-io/druid,deltaprojects/druid,winval/druid,michaelschiff/druid,praveev/druid,jon-wei/druid,andy256/druid,himanshug/druid,michaelschiff/druid,solimant/druid,metamx/druid,metamx/druid,liquidm/druid,andy256/druid,b-slim/druid,gianm/druid,gianm/druid,nishantmonu51/druid,jon-wei/druid,pjain1/druid,implydata/druid,gianm/druid,gianm/druid,monetate/druid,deltaprojects/druid,lizhanhui/data_druid,leventov/druid,taochaoqiang/druid,leventov/druid,monetate/druid,implydata/druid,deltaprojects/druid,himanshug/druid,knoguchi/druid,liquidm/druid,michaelschiff/druid,metamx/druid,implydata/druid,b-slim/druid,leventov/druid,Fokko/druid,monetate/druid,monetate/druid,Fokko/druid,monetate/druid,praveev/druid,himanshug/druid,leventov/druid,michaelschiff/druid,andy256/druid,nishantmonu51/druid,monetate/druid,andy256/druid,himanshug/druid,nishantmonu51/druid,lizhanhui/data_druid,dkhwangbo/druid,solimant/druid,dkhwangbo/druid,Fokko/druid,mghosh4/druid,nishantmonu51/druid,pjain1/druid,liquidm/druid,nishantmonu51/druid,deltaprojects/druid,pjain1/druid,mghosh4/druid,monetate/druid,druid-io/druid,b-slim/druid,dkhwangbo/druid,taochaoqiang/druid,solimant/druid,praveev/druid,deltaprojects/druid,taochaoqiang/druid,mghosh4/druid,b-slim/druid,winval/druid,pjain1/druid,jon-wei/druid,metamx/druid,leventov/druid,b-slim/druid,druid-io/druid,jon-wei/druid,winval/druid,michaelschiff/druid,andy256/druid,jon-wei/druid,implydata/druid,pjain1/druid,himanshug/druid,implydata/druid,Fokko/druid,implydata/druid,mghosh4/druid,taochaoqiang/druid,pjain1/druid,pjain1/druid,knoguchi/druid,lizhanhui/data_druid,winval/druid,lizhanhui/data_druid,michaelschiff/druid,liquidm/druid,knoguchi/druid,mghosh4/druid,mghosh4/druid,jon-wei/druid,nishantmonu51/druid,jon-wei/druid,winval/druid,dkhwangbo/druid,liquidm/druid,knoguchi/druid,solimant/druid,dkhwangbo/druid,lizhanhui/data_druid,praveev/druid,Fokko/druid,deltaprojects/druid,Fokko/druid,knoguchi/druid,liquidm/druid,michaelschiff/druid,solimant/druid,gianm/druid,Fokko/druid,gianm/druid,metamx/druid,mghosh4/druid,druid-io/druid,deltaprojects/druid,gianm/druid,praveev/druid,druid-io/druid