Added test for failed HTTP executor authentication.
Added test for failed HTTP executor authentication.

This patch adds a new test, `SlaveTest.HTTPExecutorBadAuthentication`,
which verifies that an HTTP executor cannot subscribe or launch nested
containers when it provides an authentication token that has not been
properly signed.

Review: https://reviews.apache.org/r/58624/

abudnik/mesos,gsantovena/mesos,dforsyth/mesos,neilconway/mesos,neilconway/mesos,gsantovena/mesos,gsantovena/mesos,Gilbert88/mesos,andschwa/mesos,asamerh4/mesos,Gilbert88/mesos,neilconway/mesos,verizonlabs/mesos,kaysoky/mesos,neilconway/mesos,zmalik/mesos,verizonlabs/mesos,chhsia0/mesos,abudnik/mesos,jpeach/mesos,jpeach/mesos,zmalik/mesos,kaysoky/mesos,abudnik/mesos,verizonlabs/mesos,abudnik/mesos,Gilbert88/mesos,reneploetz/mesos,abudnik/mesos,gsantovena/mesos,reneploetz/mesos,Gilbert88/mesos,andschwa/mesos,neilconway/mesos,asamerh4/mesos,jpeach/mesos,chhsia0/mesos,zmalik/mesos,abudnik/mesos,kaysoky/mesos,neilconway/mesos,verizonlabs/mesos,asamerh4/mesos,abudnik/mesos,asamerh4/mesos,verizonlabs/mesos,reneploetz/mesos,reneploetz/mesos,dforsyth/mesos,jpeach/mesos,chhsia0/mesos,reneploetz/mesos,reneploetz/mesos,jpeach/mesos,kaysoky/mesos,dforsyth/mesos,neilconway/mesos,Gilbert88/mesos,chhsia0/mesos,kaysoky/mesos,zmalik/mesos,andschwa/mesos,andschwa/mesos,jpeach/mesos,dforsyth/mesos,kaysoky/mesos,Gilbert88/mesos,dforsyth/mesos,Gilbert88/mesos,reneploetz/mesos,kaysoky/mesos,verizonlabs/mesos,andschwa/mesos,asamerh4/mesos,chhsia0/mesos,zmalik/mesos,chhsia0/mesos,chhsia0/mesos,andschwa/mesos,gsantovena/mesos,zmalik/mesos,verizonlabs/mesos,asamerh4/mesos,dforsyth/mesos,andschwa/mesos,gsantovena/mesos,asamerh4/mesos,dforsyth/mesos,gsantovena/mesos,zmalik/mesos,jpeach/mesos