Add web UI routing support
Add web UI routing support

Route the calls that a browser will request when
it's pointed at https://<bmc> to the specified
files in /usr/share/www, which come from the
phosphor-webui repository.

This takes over the '/' REST endpoint, but that provides
no functionality to the customer anyway.

The long term vision is to use a more advanced server
like nginx, but this is needed until something else is ready.

Tested: Served the phosphor-webui GUI from the BMC with
the script.

Resolves openbmc/openbmc#2821

Change-Id: Id491f9e0865a445160b91897082eb1c69695f562
Signed-off-by: Matt Spinler <c000c989d08c98662d98f15448f11de169feb92d@us.ibm.com>

openbmc/phosphor-rest-server,openbmc/phosphor-rest-server