Add support for non-A/B OTA package in OTA_analysis.

The non-A/B OTA package has a very different file system compared with
an OTA package. However, our OTA_analysis tool is based on the
update_metadata.proto. What we do here is try to convert the non-A/B OTA
package information, into a standard update_metadata.proto formated
manifest. The format and how the conversion works can be found in this
document:
https://docs.google.com/document/d/e/2PACX-1vRwMRodq4TCvTPEmlU6KL9vPSeFmEJjVXzq4PHhrB8tGy6oHFDJGCk3bIDA5Uv-4UEP0stLarBlhl2c/pub

In this CL, most of the information is successfully parsed, except
installation ops like stash, free, bsdiff, imgdiff, move. (anything
related to stash is not yet implemented)

Test: test by selecting a non-A/B OTA package.
Change-Id: I298f238395478422daece47cedbaa52a976d9f4c
8 files changed