pgsql: Cover additional errors and corner conditions in repack.c

Cover additional errors and corner conditions in repack.c

The coverage report shows that some error cases were not being tested;
add test cases for them.

While at it, move some recently added ones to the test_decoding suite:
the preventative check added in 43649b6a53e9 now causes servers with
wal_level=minimal to error out earlier than before.

Author: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Reviewed-by: Baji Shaik <baji(dot)pgdev(at)gmail(dot)com>
Discussion: https://postgr.es/m/ahiwD29RNfVT4tjQ@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2670cc298f42cd7b1c426bf7ccfb0652d8e0b347

Modified Files
--------------
contrib/test_decoding/expected/repack.out | 50 ++++++++++++++++++
contrib/test_decoding/sql/repack.sql | 43 +++++++++++++++
src/test/regress/expected/cluster.out | 87 ++++++++++++-------------------
src/test/regress/sql/cluster.sql | 73 ++++++++++----------------
4 files changed, 154 insertions(+), 99 deletions(-)