Fix tests for MirroredBufferPool_Truncate() invocation
Fix tests for MirroredBufferPool_Truncate() invocation

MirroredBufferedPool_Truncate() returns a boolean so testing for
(!returnvalue < 0) will always return false and not what we expect
it to test.

Github user fengttt.

chrishajas/gpdb,rvs/gpdb,Chibin/gpdb,rubikloud/gpdb,xuegang/gpdb,zaksoup/gpdb,ahachete/gpdb,ahachete/gpdb,lintzc/gpdb,chrishajas/gpdb,lintzc/gpdb,randomtask1155/gpdb,tangp3/gpdb,yuanzhao/gpdb,lpetrov-pivotal/gpdb,rubikloud/gpdb,Quikling/gpdb,randomtask1155/gpdb,Quikling/gpdb,xuegang/gpdb,kaknikhil/gpdb,janebeckman/gpdb,janebeckman/gpdb,tangp3/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,xuegang/gpdb,lisakowen/gpdb,lpetrov-pivotal/gpdb,yuanzhao/gpdb,Chibin/gpdb,0x0FFF/gpdb,CraigHarris/gpdb,xinzweb/gpdb,Chibin/gpdb,ahachete/gpdb,xinzweb/gpdb,ahachete/gpdb,50wu/gpdb,ahachete/gpdb,ahachete/gpdb,kaknikhil/gpdb,Quikling/gpdb,adam8157/gpdb,ashwinstar/gpdb,rvs/gpdb,rvs/gpdb,greenplum-db/gpdb,lintzc/gpdb,Chibin/gpdb,randomtask1155/gpdb,CraigHarris/gpdb,janebeckman/gpdb,tangp3/gpdb,janebeckman/gpdb,lintzc/gpdb,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,jmcatamney/gpdb,tangp3/gpdb,rubikloud/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,rubikloud/gpdb,royc1/gpdb,janebeckman/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,randomtask1155/gpdb,Quikling/gpdb,Chibin/gpdb,adam8157/gpdb,0x0FFF/gpdb,lpetrov-pivotal/gpdb,tangp3/gpdb,adam8157/gpdb,yuanzhao/gpdb,lintzc/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,edespino/gpdb,zaksoup/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,tangp3/gpdb,janebeckman/gpdb,Quikling/gpdb,chrishajas/gpdb,lisakowen/gpdb,jmcatamney/gpdb,lintzc/gpdb,lisakowen/gpdb,xuegang/gpdb,edespino/gpdb,janebeckman/gpdb,ahachete/gpdb,lisakowen/gpdb,edespino/gpdb,xinzweb/gpdb,CraigHarris/gpdb,lpetrov-pivotal/gpdb,Chibin/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,adam8157/gpdb,Chibin/gpdb,50wu/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,Chibin/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,royc1/gpdb,lisakowen/gpdb,xuegang/gpdb,edespino/gpdb,kaknikhil/gpdb,tangp3/gpdb,randomtask1155/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,CraigHarris/gpdb,janebeckman/gpdb,lisakowen/gpdb,royc1/gpdb,rvs/gpdb,cjcjameson/gpdb,Quikling/gpdb,50wu/gpdb,rvs/gpdb,lpetrov-pivotal/gpdb,50wu/gpdb,yuanzhao/gpdb,rvs/gpdb,cjcjameson/gpdb,zaksoup/gpdb,chrishajas/gpdb,rvs/gpdb,kaknikhil/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,xinzweb/gpdb,randomtask1155/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,Quikling/gpdb,randomtask1155/gpdb,xuegang/gpdb,edespino/gpdb,zaksoup/gpdb,0x0FFF/gpdb,CraigHarris/gpdb,xinzweb/gpdb,chrishajas/gpdb,royc1/gpdb,Chibin/gpdb,ashwinstar/gpdb,0x0FFF/gpdb,royc1/gpdb,rvs/gpdb,rubikloud/gpdb,chrishajas/gpdb,chrishajas/gpdb,ahachete/gpdb,xuegang/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,edespino/gpdb,rubikloud/gpdb,yuanzhao/gpdb,edespino/gpdb,xinzweb/gpdb,yuanzhao/gpdb,lintzc/gpdb,yuanzhao/gpdb,zaksoup/gpdb,50wu/gpdb,royc1/gpdb,lisakowen/gpdb,rubikloud/gpdb,lisakowen/gpdb,CraigHarris/gpdb,edespino/gpdb,cjcjameson/gpdb,ashwinstar/gpdb,xuegang/gpdb,lintzc/gpdb,50wu/gpdb,kaknikhil/gpdb,zaksoup/gpdb,randomtask1155/gpdb,Chibin/gpdb,0x0FFF/gpdb,adam8157/gpdb,zaksoup/gpdb,cjcjameson/gpdb,lintzc/gpdb,janebeckman/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,royc1/gpdb,50wu/gpdb,edespino/gpdb,cjcjameson/gpdb,royc1/gpdb,xinzweb/gpdb,tangp3/gpdb,Quikling/gpdb,adam8157/gpdb,xuegang/gpdb,cjcjameson/gpdb,lpetrov-pivotal/gpdb,lpetrov-pivotal/gpdb,chrishajas/gpdb,jmcatamney/gpdb,zaksoup/gpdb,0x0FFF/gpdb,janebeckman/gpdb,ashwinstar/gpdb,50wu/gpdb,Quikling/gpdb,ashwinstar/gpdb,rvs/gpdb,rubikloud/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,Quikling/gpdb,edespino/gpdb,adam8157/gpdb