pgsql: Add TAP tests for pg_verify_checksums

Add TAP tests for pg_verify_checksums

All options available in the utility get coverage:
- Tests with disabled page checksums.
- Tests with enabled test checksums.
- Emulation of corruption and broken checksums with a full scan and
single relfilenode scan.

This patch has been contributed mainly by Michael Banck and Magnus
Hagander with things presented on various threads, and I have gathered
all the contents into a single patch.

Author: Michael Banck, Magnus Hagander, Michael Paquier
Reviewed-by: Peter Eisentraut
Discussion: https://postgr.es/m/20181005012645.GE1629@paquier.xyz

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/b34e84f160a47d9070b304bfc1baf17596d71865

Modified Files
--------------
src/bin/initdb/t/001_initdb.pl               | 14 +++++-
src/bin/pg_verify_checksums/.gitignore       |  2 +
src/bin/pg_verify_checksums/Makefile         |  6 +++
src/bin/pg_verify_checksums/t/001_basic.pl   |  8 ++++
src/bin/pg_verify_checksums/t/002_actions.pl | 69 ++++++++++++++++++++++++++++
5 files changed, 98 insertions(+), 1 deletion(-)