pgsql: Improve test coverage of pg_rewind

Improve test coverage of pg_rewind

This includes new TAP tests for a couple of areas not covered yet and
some improvements:
- More coverage for --no-ensure-shutdown, the enforced recovery step and
--dry-run.
- Failures with option combinations and basic option checks.
- Removal of a duplicated comment.

Author: Alexey Kondratov, Michael Paquier
Discussion: https://postgr.es/m/20191007010651.GD14532@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/55ba56415bae6ac1f43c12d54537bd60eaa2153b

Modified Files
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src/bin/pg_rewind/t/001_basic.pl         | 67 +++++++++++++++++++++++++++++++-
src/bin/pg_rewind/t/005_same_timeline.pl |  3 --
src/bin/pg_rewind/t/006_options.pl       | 40 +++++++++++++++++++
3 files changed, 106 insertions(+), 4 deletions(-)