Change launcher working directory before dropping privilege.
Change launcher working directory before dropping privilege.

The launcher needs to change its working directory before dropping
privilege by switching users and installing capabilities, because
afterwards it might not have access to traverse to the desired
working directory.

Review: https://reviews.apache.org/r/59551/

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