Add a demo page in OTA_analyzer.

Please put an ota package and its target build as cf_x86_demo.zip and
cf_x86_target_file_demo into this directory: /public/files/

This OTA package and target build do not have to be complete - only the
manifest part in OTA package and .map files in target build are
necessary. The previous one can be generated using:
https://source.corp.google.com/android/vendor/google_tradefederation/contrib/src/com/google/android/tradefed/ota/util/PayloadUtil.java;l=196;bpv=1;bpt=1?q=PayloadUtil&sq=package:android
The following one can be generated by unzip and keep the .map files
only, zip again.

Add a demo page, now the user can view the complete function of
OTA_analyzer without uploading their own ota packages / android build.

Test: Mannual tested.
Change-Id: I7552e0222fc40e9a4b1aff9750f74cd3ed3f4feb
5 files changed