Fixed a file descriptor leak in io::peek().
Fixed a file descriptor leak in io::peek().

Review: https://reviews.apache.org/r/38780

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