isolation2: Initial attempt to parallel schedule.
isolation2: Initial attempt to parallel schedule.

Isolation2 schedule is completely serial currently. Seeking motivation from
upstream discussion to parallelize isolation schedule
(http://www.postgresql-archive.org/reducing-isolation-tests-runtime-td6002684.html)
tried for isolation2 and it works for these tests. Cuts down time to 4 secs from
11 secs (serially) on my laptop. (We currently have very few tests in isolation
which run under 1 sec so not very useful there.)

Need to carefull look at other tests and schedule can be rearranged to make more
tests run in parallel group. Just wish to open this up before moving further.

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