sstableloader: Fix verbose level parsing
sstableloader: Fix verbose level parsing

Allow optional verbose levels on command line.

Message-Id: <ce7648b48ff9a41e9a03038969dc4196c44b8af7@scylladb.com>

scylladb/scylla-tools-java,scylladb/scylla-tools-java,scylladb/scylla-tools-java,scylladb/scylla-tools-java