pgsql: Add more tests for FSM.

Add more tests for FSM.

In commit b0eaa4c51bb, we left out a test that used a vacuum to remove dead
rows as the behavior of test was not predictable. This test has been
rewritten to use fillfactor instead to control free space. Since we no
longer need to remove dead rows as part of the test, put the fsm regression
test in a parallel group.

Author: John Naylor
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1L=qWp_bJ5aTc9+fy4Ewx2LPaLWY-RbR4a60g_rupCKnQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/6f918159a97acf76ee2512e44f5ed5dcaaa0d923

Modified Files
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src/test/regress/expected/fsm.out | 59 +++++++++++++++++++++++++++-----------
src/test/regress/parallel_schedule | 8 +-----
src/test/regress/serial_schedule | 2 +-
src/test/regress/sql/fsm.sql | 41 ++++++++++++++++++++------
4 files changed, 77 insertions(+), 33 deletions(-)