pr_pipeline: set max_in_flight
pr_pipeline: set max_in_flight

This helps in predictably managing load on concourse.

Signed-off-by: David Sharp <2664301c0a809f94c834d0a9c6cef510e103d89b@pivotal.io>

janebeckman/gpdb,greenplum-db/gpdb,rvs/gpdb,cjcjameson/gpdb,Quikling/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,Chibin/gpdb,jmcatamney/gpdb,rvs/gpdb,Quikling/gpdb,50wu/gpdb,cjcjameson/gpdb,edespino/gpdb,lisakowen/gpdb,edespino/gpdb,50wu/gpdb,edespino/gpdb,Quikling/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,Quikling/gpdb,adam8157/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,edespino/gpdb,edespino/gpdb,janebeckman/gpdb,greenplum-db/gpdb,rvs/gpdb,kaknikhil/gpdb,edespino/gpdb,xinzweb/gpdb,lisakowen/gpdb,Quikling/gpdb,50wu/gpdb,yuanzhao/gpdb,lisakowen/gpdb,Chibin/gpdb,yuanzhao/gpdb,50wu/gpdb,adam8157/gpdb,yuanzhao/gpdb,xinzweb/gpdb,ashwinstar/gpdb,janebeckman/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,xinzweb/gpdb,Chibin/gpdb,50wu/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,50wu/gpdb,janebeckman/gpdb,Chibin/gpdb,ashwinstar/gpdb,Chibin/gpdb,lisakowen/gpdb,adam8157/gpdb,Quikling/gpdb,jmcatamney/gpdb,adam8157/gpdb,kaknikhil/gpdb,lisakowen/gpdb,Chibin/gpdb,xinzweb/gpdb,Chibin/gpdb,rvs/gpdb,Chibin/gpdb,Quikling/gpdb,janebeckman/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,rvs/gpdb,xinzweb/gpdb,janebeckman/gpdb,rvs/gpdb,adam8157/gpdb,cjcjameson/gpdb,Chibin/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,xinzweb/gpdb,50wu/gpdb,Chibin/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,janebeckman/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,janebeckman/gpdb,greenplum-db/gpdb,janebeckman/gpdb,xinzweb/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,lisakowen/gpdb,ashwinstar/gpdb,edespino/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,Quikling/gpdb,kaknikhil/gpdb,xinzweb/gpdb,greenplum-db/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,50wu/gpdb,edespino/gpdb,edespino/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,adam8157/gpdb,rvs/gpdb,rvs/gpdb,rvs/gpdb,adam8157/gpdb,lisakowen/gpdb,edespino/gpdb,greenplum-db/gpdb,lisakowen/gpdb,Quikling/gpdb,yuanzhao/gpdb,rvs/gpdb,Quikling/gpdb,adam8157/gpdb,janebeckman/gpdb,cjcjameson/gpdb