fix(nonroot offline install): fetch scylla-server log from the redirected file
fix(nonroot offline install): fetch scylla-server log from the redirected file

Scylla-server log was redirected to ~/scylladb/scylla-server.log after
scylladb/scylla@0f786f0.

So current 'journalctl' cmdline can't fetch the scylla-server log, the
log file in test result is empty.

This patch changed to fetch scylla-server log from different source for
nonroot offline install.

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>

scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests