fs_config_generate: add -P <partitionlist> option

Add a -P option to fs_config_generate that allows us to filter on
a comma separated partition whitelist or minus prefixed -blacklist.
A partition is defined as accessible as <partition>/ or
system/<partition>/.

No change for legacy, where no -P flag is specified.

For system.img, but not vendor, oem or odm file references:
fs_config_generate -P -vendor,-oem,-odm

For vendor.img file references:
fs_config_generate -P vendor

For oem.img file references:
fs_config_generate -P oem

For odm.img file references:
fs_config_generate -P odm

Add and fortify tests for each of these cases.

SideEffects: none
Test: gTest host fs_config-unit-test
Bug: 36071012
Change-Id: I0537453bb289d41ef98ad76e69f78ae49358a1b3