Used execlp instead of execl to exec processes in libprocess.
Used execlp instead of execl to exec processes in libprocess.

Review: https://reviews.apache.org/r/37546

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