Modify string format in BRILLO_VENDOR_PARTITIONS to preserve path.

BRILLO_VENDOR_PARTITIONS contains a list of strings in the format of
parent_folder:file_path. Each vendor partition's full path is
parent_folder/file_path. The directory structure in file_path will be preserved.

Bug: 25692226
TEST: local run m dist, confirm dragonboard-vendor_partitions-eng.dshi.zip
created in out/dist, and content is correct.

Change-Id: Icff46e4fa797cb6df7a2b8a651c6879c792cb60e
1 file changed