services: reports: serve reports ui xml as servlet

instead of using direct static content which does not support logic, use
a servlet that can acquire information from whatever source.

in this patch the source is local config, to allow easy integration with
reports without reports package overwrite the engine data directory.

currently we put the reports.xml at package state, so it can be added
and removed without restarting engine, this may change in future.

Change-Id: I78f7822354ac6850a49698b0262209489a5ab5b3
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>