Allow map_file_generator to use host tools

map_file_generator need to invoke binaries such as `unsquashfs` .
These binaries are built from android source tree, so add host binary
output directory to PATH variable so that map_file_generator can use
these binaries.

Test: th
Bug: 286870582
Change-Id: I56634293ee885fc4612627578a22cdf57bc13bfc