Plot with legend_label option to remove BokehDeprecationWarnings

[reoono]

FIx #131

To remove BokehDeprecationWarnings, we changed the legend option to legend_label. It can suppress warnings by environment variables such as BOKEH_PY_LOG_LEVEL. But to follow API changes, we created this PR.

To be sure, we also tried other options and found the following errors and display errors, so we do not think there is a problem with the modification.

• 'legend_field'.

  ERROR:bokeh.core.validation.check:E-1001 (BAD_COLUMN_NAME): Glyph refers to nonexistent column name. This could either be due to a misspelling or typo, or due to an expected column being missing.
  ...

• 'legend_group'.

  ERROR:tornado.application:Uncaught exception GET /Machine-Resources (127.0.0.1)
  HTTPServerRequest(protocol='http', host='127.0.0.1:9090', method='GET', uri='/Machine-Resources', version='HTTP/1.1', remote_ip='127.0.0.1')
  Traceback (most recent call last):
  ...

[GPUtester]

Can one of the admins verify this patch?

[jacobtomlinson]

ok to test