Add framework's pid to json summary of framework.
Add framework's pid to json summary of framework.

Following pattern of slave exposing its pid.

Review: https://reviews.apache.org/r/34371

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