Update sysctl settings to match new recommendations
Update sysctl settings to match new recommendations

The recommended sysctl settings for user clusters are out-of-date, and
after some investigation we've discovered a good minimal set of
recommended defaults.  These will be updated in the documentation, but
we also want to set them in the VMs used for our CLI Behave tests so
that we use values similar to those that users will have in their
environments, so this commit adds a section to the Concourse cluster
task file to do so.

Co-authored-by: Jamie McAtamney <62a39b9671f8c44911ae4c7f4452af6da0c5d67e@pivotal.io>
Co-authored-by: Kalen Krempely <9e21ad9b1cb949be1035df9e3f38e74e41b67a0b@pivotal.io>
Co-authored-by: Nikolaos Kalampalikis <c999ff058776a87612af1f602e9eec50c233885e@pivotal.io>

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