build-from-source: fix build failure due to netconfig path

During the test build we enabled "--with-netconfig=yes".

Since commit "5b36585a3d build/autotools: fail configure if
netconfig/resolveconf tool is not found", when specifying
"--with-netconfig=yes" the user is required to have netconfig
installed (so that the path can be detected). Otherwise it fails
with

    checking for netconfig... no
    configure: error: cannot find netconfig in path. Set the path explicitly via --with-netconfig=PATH.

The correct way is to explicitly specify the path. In that
case, it's OK that the file doesn't actually exist.

contrib/rh-bkr/build-from-source.sh

@@ -119,7 +119,8 @@ if [[ "$DO_TEST_BUILD" == yes ]]; then
         --with-suspend-resume=systemd \
         --enable-teamdctl=yes \
         --enable-tests=root \
-        --with-netconfig=yes \
+        --with-netconfig=/path/does/not/exist/netconfig \
+        --with-resolvconf=/path/does/not/exist/resolvconf \
         --with-crypto=nss \
         --with-session-tracking=systemd \
         --with-consolekit=yes \