Bug report

Bug summary

Hardcoded URL in webagg backend is misleading and sometimes wrong

Code for reproduction

importmatplotlibasmplmpl.use('WebAgg')importmatplotlib.pyplotaspltimportnumpyasnpmpl.rcParams['webagg.open_in_browser']=Falsefig,plot=plt.subplots(nrows=1)plot.imshow(np.random.rand(224,224,3))plt.show()

Actual outcome

To view figure, visit http://127.0.0.1:8988Press Ctrl+C to stop WebAgg server

Expected outcome

Hopefully something like

To view figure, visit http://[insert my server IP here]:8988Press Ctrl+C to stop WebAgg server

Matplotlib version

• Operating system: Ubuntu 16.04
• Matplotlib version: 2.0.2
• Matplotlib backend (print(matplotlib.get_backend())): WebAgg
• Python version: 3.6.1
• Jupyter version (if applicable):
• Other libraries:

Basically, it'd be nice to have control over what IP gets printed there, instead of hard coding localhost --https://github.com/matplotlib/matplotlib/blob/master/lib/matplotlib/backends/backend_webagg.py#L324 -- maybe add another key to rcParams? (and leave localhost as the default?)