Make --scale a mandatory option in single_node_perf_run.py

Traceback (most recent call last):
  File "./bin/run-workload.py", line 257, in <module>
    workload_runners.append(WorkloadRunner(workload, scale_factor, config))
  File "./tests/performance/workload_runner.py", line 71, in __init__
    self._generate_test_vectors()
  File "./tests/performance/workload_runner.py", line 88, in _generate_test_vectors
    self._test_vectors.append(TableFormatInfo.create_from_string(dataset, tf))
  File "./tests/common/test_dimensions.py", line 70, in create_from_string
    raise ValueError, 'Invalid table format %s' % table_format_string
ValueError: Invalid table format kudu 
Traceback (most recent call last):
  File "./bin/single_node_perf_run.py", line 348, in <module>
    main()
  File "./bin/single_node_perf_run.py", line 338, in main
    perf_ab_test(options, args)
  File "./bin/single_node_perf_run.py", line 230, in perf_ab_test
    build(hash_a, options)
  File "./bin/single_node_perf_run.py", line 111, in build
    configured_call(buildall)
  File "./bin/single_node_perf_run.py", line 87, in configured_call
    return subprocess.check_call(["bash", "-c", cmd])
  File "/usr/lib/python2.7/subprocess.py", line 541, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['bash', '-c', 'source ./bin/impala-config.sh && ./buildall.sh -notests -release -noclean']' returned non-zero exit status 2

AnalysisException: Database does not exist: tpchNone_kudu