system_queries: Migrate system queries into a single place

This provides better separation of the DBus interface and the underlying
system interactions.

Change-Id: I8bf7a44c679ab065f959af19a00c29897c1d5c48
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/mock_syscall.cpp b/test/mock_syscall.cpp
index 349a79a..e5f97be 100644
--- a/test/mock_syscall.cpp
+++ b/test/mock_syscall.cpp
@@ -181,9 +181,7 @@
 int getifaddrs(ifaddrs** ifap)
 {
     *ifap = mock_ifaddrs;
-    if (mock_ifaddrs == nullptr)
-        return -1;
-    return (0);
+    return 0;
 }
 
 unsigned if_nametoindex(const char* ifname)