qa/rgw: fix perl tests missing Amazon::S3 module

qa/rgw: fix perl tests missing Amazon::S3 module

and a second case where perl tests can fail without error output

1. fix errors like: `Can't locate Amazon/S3.pm in @INC (you may need to
   install the Amazon::S3 module)`
by priming the perl tests with installing the Amazon::S3 module from cpan

ex:
```
2025-06-23T19:18:40.162 INFO:tasks.workunit.client.0.smithi090.stderr:Can't locate Amazon/S3.pm in @INC (you may need to install the Amazon::S3 module) (@INC contains: /usr/local/lib64/perl5/5.32 ...
```

2. log an error when RGW process is not detected

Fixes: https://tracker.ceph.com/issues/71577
Signed-off-by: Mark Kogan <mkogan@redhat.com>