Fixed some issues in newbie-guide.md.
Fixed some issues in newbie-guide.md.

Fixes issues within the newbie-guide including the removal of a
reference to a non-existent image (see MESOS-5292 for details).

Review: https://reviews.apache.org/r/47115/

neilconway/mesos,yuquanshan/customizedMesos,chhsia0/mesos,andschwa/mesos,yuquanshan/customizedMesos,Aman-Jain-14/customizedMesos,jpeach/mesos,reneploetz/mesos,yuquanshan/customizedMesos,asamerh4/mesos,neilconway/mesos,zmalik/mesos,chhsia0/mesos,gsantovena/mesos,asamerh4/mesos,Gilbert88/mesos,verizonlabs/mesos,Aman-Jain-14/customizedMesos,craimbert/mesos,andschwa/mesos,craimbert/mesos,chhsia0/mesos,Gilbert88/mesos,asamerh4/mesos,andschwa/mesos,verizonlabs/mesos,gsantovena/mesos,verizonlabs/mesos,dforsyth/mesos,kaysoky/mesos,verizonlabs/mesos,neilconway/mesos,Gilbert88/mesos,dforsyth/mesos,abudnik/mesos,reneploetz/mesos,Gilbert88/mesos,gsantovena/mesos,gsantovena/mesos,craimbert/mesos,andschwa/mesos,verizonlabs/mesos,reneploetz/mesos,yuquanshan/customizedMesos,jpeach/mesos,zmalik/mesos,kaysoky/mesos,dforsyth/mesos,Aman-Jain-14/customizedMesos,verizonlabs/mesos,abudnik/mesos,andschwa/mesos,neilconway/mesos,asamerh4/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,dforsyth/mesos,zmalik/mesos,verizonlabs/mesos,abudnik/mesos,yuquanshan/customizedMesos,jpeach/mesos,jpeach/mesos,kaysoky/mesos,chhsia0/mesos,zmalik/mesos,abudnik/mesos,zmalik/mesos,dforsyth/mesos,jpeach/mesos,kaysoky/mesos,craimbert/mesos,neilconway/mesos,Aman-Jain-14/customizedMesos,dforsyth/mesos,asamerh4/mesos,craimbert/mesos,gsantovena/mesos,kaysoky/mesos,abudnik/mesos,gsantovena/mesos,kaysoky/mesos,craimbert/mesos,reneploetz/mesos,Gilbert88/mesos,zmalik/mesos,andschwa/mesos,abudnik/mesos,gsantovena/mesos,yuquanshan/customizedMesos,chhsia0/mesos,abudnik/mesos,kaysoky/mesos,asamerh4/mesos,reneploetz/mesos,jpeach/mesos,reneploetz/mesos,Aman-Jain-14/customizedMesos,jpeach/mesos,neilconway/mesos,chhsia0/mesos,yuquanshan/customizedMesos,Gilbert88/mesos,zmalik/mesos,reneploetz/mesos,Aman-Jain-14/customizedMesos,Gilbert88/mesos,neilconway/mesos,chhsia0/mesos,asamerh4/mesos,craimbert/mesos,andschwa/mesos