Fix storage test failures caused by 916f460
Fix storage test failures caused by 916f460

The default value of Gp_role is set to GP_ROLE_DISPATCH. Which means
auxiliary processes inherit this value. FileRep does the same, but also
executes queries using SPI on the segment. Which means Gp_role ==
GP_ROLE_DISPATCH is not a sufficient check for master QD.

So, bring back the check on GpIdentity.

Author: Asim R P <24f343109504afa210657d296a0873118cbd2b97@pivotal.io>
Author: Shreedhar Hardikar <a657aa6fe6df17a9d181476831de52530bd87b81@pivotal.io>

xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,xinzweb/gpdb,greenplum-db/gpdb,Chibin/gpdb,50wu/gpdb,Chibin/gpdb,adam8157/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,yuanzhao/gpdb,lisakowen/gpdb,50wu/gpdb,Chibin/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,50wu/gpdb,Chibin/gpdb,Chibin/gpdb,edespino/gpdb,adam8157/gpdb,xinzweb/gpdb,edespino/gpdb,50wu/gpdb,ashwinstar/gpdb,edespino/gpdb,edespino/gpdb,edespino/gpdb,yuanzhao/gpdb,Chibin/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,lisakowen/gpdb,edespino/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,Chibin/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,xinzweb/gpdb,50wu/gpdb,ashwinstar/gpdb,edespino/gpdb,xinzweb/gpdb,adam8157/gpdb,ashwinstar/gpdb,Chibin/gpdb,adam8157/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,adam8157/gpdb,xinzweb/gpdb,50wu/gpdb,yuanzhao/gpdb,lisakowen/gpdb,edespino/gpdb,lisakowen/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,lisakowen/gpdb,yuanzhao/gpdb,Chibin/gpdb,50wu/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,xinzweb/gpdb,ashwinstar/gpdb,adam8157/gpdb,edespino/gpdb,Chibin/gpdb,adam8157/gpdb,yuanzhao/gpdb,lisakowen/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,edespino/gpdb,greenplum-db/gpdb