pgsql: Deal with paths containing \ and spaces in basebackup_to_shell t

Deal with paths containing \ and spaces in basebackup_to_shell tests

As $gzip is embedded in postgresql.conf \ needs to be escaped, otherwise guc.c
will take it as a string escape. Similarly, if "$gzip" contains spaces, the
prior incantation will fail. Both of these are common on windows.

Reviewed-by: Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com>
Discussion: https://postgr.es/m/ce1b6eb3-5736-6f38-9775-b7020128b8d8@enterprisedb.com
Backpatch: 15-, where the test was added in 027fa0fd726

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a91242b1bcb312d6f482a758a432a32bd375896e

Modified Files
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contrib/basebackup_to_shell/t/001_basic.pl | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)