Added functionality in soong_zip that supports adding root prefix.

Added -P flag in soong_zip:
It provided a path prefix which will be added in front after -f/-l was
applied with -C.

eg. ./soong_zip -o /path1/../ -P a/c -C d/e -f d/e/test.txt

zip_dest: a/c/test.txt

Bug: b/31676493
Test: go build -a to build a real soong_zip, and test it with real
files.
Change-Id: Ic924ba252e963ca5847c370f733058888426b696