Added SchedulerHttpApiTest.UpdateHttpToPidSchedulerAndBack test.
Added SchedulerHttpApiTest.UpdateHttpToPidSchedulerAndBack test.

This test verifies that we are able to upgrade from a PID based
framework to an HTTP framework and then downgrade back without
restarting the master.

Review: https://reviews.apache.org/r/62241/

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