roachtest: disable cluster reuse for sysbench/postgres* tests

[DarrylWong]

Installing postgres creates a lot of directories that are not properly cleaned up by a cluster wipe. Disable cluster reuse
to avoid any side effects.

Release note: none
Fixes: #149127
Fixes: #149126
Fixes: #149128

[cockroach-teamcity]

This change is 

[DarrylWong]

I tried a combination of:

sudo rm -rf /var/lib/postgresql/
sudo rm -rf /var/lib/postgresql.bak/
sudo apt-get --purge -y remove postgresql postgresql-*

but kept finding more and more directories that needed to be removed. Opted to just disable cluster reuse since cleanup seemed error prone, but fyi @tbg in case you have any strong opinions.

[tbg]

Yeah, no point in reusing the postgres clusters - we should just give them fresh clusters. Sorry about the noise, and thank you for looking.

[DarrylWong]

TFTR!

bors r=tbg

[craig]

Build succeeded:

• examples_orms
• unit_tests
• docker_image_amd64
• local_roachtest
• acceptance
• check_generated_code
• linux_amd64_build
• local_roachtest_fips
• linux_amd64_fips_build
• lint