Add CHECK_FOR_INTERRUPTS before reading a page from disk
Add CHECK_FOR_INTERRUPTS before reading a page from disk

This came in as a suggestion from Aswhin on the discussion:
https://groups.google.com/a/greenplum.org/d/msg/gpdb-dev/S2WL1FtJEJ0/Wh6DfJ-RBwAJ

The patch does not have any tests because simulating that a reader
checked for interrupts(SIGINT) before reading a page into shared
buffers requires co-ordination with the writer and the QD. This
requires adding multiple fault injectors and doesn't seem worth the
effort.

Co-authored-by: Asim R P <24f343109504afa210657d296a0873118cbd2b97@pivotal.io>

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