syscall_filter: Add better error reporting.

Add error messages and tests for:

-Empty atoms.
-Invalid arguments: "arg0n == 0".
-Invalid atoms: "arg0", "arg0 ==".
-Extra tokens: "arg0 == 0 EXTRATOKEN".

Also make the unit tests Valgrind-clean.

Bug: 32570874
Test: syscall_filter_unittest
Change-Id: I73ab88b51f36debe92f61fda7470e8e0d29afab5
3 files changed