Added move construction and assignment to Future.
Added move construction and assignment to Future.

Includes using `default` where applicable.

Review: https://reviews.apache.org/r/65375/

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