canned fs_config accepts multiple lines having the same path

Previously, each file/dir in a filesystem had to have exactly one
matching entry in the canned fs_config file. With this change, the
config file can have multiple entries for the same path. e.g.

/lib/libfoo.so 1000 1000 0644
/lib/libfoo.so 1000 2000 0644 capabilities=0x30

In this case, the last matching entry is chosen and used. This is to
make it possible to customize system-provided (and thus generic)
fs_config file with a user-provided (and thus context-specific) one.

Bug: 209971551
Test: m
Change-Id: I43902fed08db1b4968d02c75fac0a47976fff72a