merge_zips: fix compressed size and CRC32 fields for inserted manifests

The compressed size and CRC32 fields in the file headers were left at
0 for inserted manifests, resulting in an invalid zip file.  Insert the
compressed size and CRC32 fields anywhere the FileHeader is created
directly.

Adds tests for the merge_zips options that add files to the zip.

Test: TestMergeZips
Change-Id: Ib027f868aa6e55f848ccaaa18582ecbc54c9a8f6