FALCON-2328 Upgrade PR merge script to Python3
FALCON-2328 Upgrade PR merge script to Python3

Ran 2to3 on the script
Changed the run_cmd method to return a string rather than bytes.

Author: pallavi-rao <pallavi.rao@inmobi.com>

Reviewers: @sandeepSamudrala

Closes #404 from pallavi-rao/2328 and squashes the following commits:

0b0812c28 [pallavi-rao] FALCON-2328 Removing redundant import
3e79a3569 [pallavi-rao] FALCON-2328 Upgrade PR merge script to Python3

InMobi/falcon,nperiwal/falcon,nperiwal/falcon,apache/falcon,apache/falcon,apache/falcon,InMobi/falcon,apache/falcon,nperiwal/falcon,apache/falcon,nperiwal/falcon,InMobi/falcon,InMobi/falcon,InMobi/falcon,InMobi/falcon,nperiwal/falcon,apache/falcon,nperiwal/falcon