Add ServerAliveInterval=60 option to ssh.
Add ServerAliveInterval=60 option to ssh.

For long running commands such as gpinitstandby with a large master data
directory, the server takes a long time. Therefore, there is no acitivity from
the client to the server. If the ClientAliveInterval is set, then the server
reports a timeout after ClientAliveInterval seconds.

Setting a ServerAliveInterval value less than the ClientAliveInterval interval
forces the client to send a Null message to the server.  Hence, avoiding the
timeout.

Co-authored-by: Jamie McAtamney <62a39b9671f8c44911ae4c7f4452af6da0c5d67e@pivotal.io>
Co-authored-by: Shoaib Lari <ad045e028025f2970ed8506438710c2da1df61d5@pivotal.io>
(cherry picked from commit 675aa8e3bd1d5bb187dc93d7ba494819cadb120e)

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