Support reading output from IptablesRestoreController.

Add the ability to IptablesRestoreController to return the output
of a command. This is useful to run commands that list chains or
return counters through the ip[6]tables-restore.

Also enable unsigned-integer-overflow sanitization the unit tests
because their behaviour should be representative of actual code.
Having address sanitization enabled would have saved a fair
amount of time debugging an on-device abort() that did not affect
the tests.

Test: new unit test passes
Bug: 32323979
Change-Id: I70726ebbade0cb792aba38787c57378df177f2d8