Fix ubuntu18.04 failed pipeline jobs: create and destroy a new waiteventset in each loop of cdbgang_createGang_async() (#13494)
Fix ubuntu18.04 failed pipeline jobs: create and destroy a new waiteventset in each loop of cdbgang_createGang_async() (#13494)

My previous commit: e30909f caused the ubuntu18.04 related pipeline jobs to fail:
"ERROR","XX000","epoll_ctl() failed: No such file or directory",,,,,,,0,,"latch.c"

RCA:
The socket FDs may be changed after calling PQconnectPoll().
The official documentation said it clearly, but I ignored it before:
"Caution: do not assume that the socket remains the same across PQconnectPoll() calls."

FIX:
Create and destroy a new waiteventset in each loop, and add all FDs into it again.


greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,50wu/gpdb