pgsql: Improve TestLib::system_or_bail error reporting

Improve TestLib::system_or_bail error reporting

The original coding was not quoting the complete failing command, and it
wasn't printing the reason for the failure either.  Do both.

This is cosmetic only, so no backpatch.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/202106301524.eq5pblzstapj@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5798ca529935698ab976780565fb2b4d8d34d810

Modified Files
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src/test/perl/TestLib.pm | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)