Fixed Python dependency pinning.
Fixed Python dependency pinning.

Without PACKAGE_VERSION specified, pypi may install more recent
Python libraries if they heppen to exist.

Signed-off-by: Chengwei Yang <yangchengwei@qiyi.com>

This closes #192

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