Use journald as the systems logging daemon

Use systemd's journald as the systems logging daemon.
See go/improve-cros-logging for details.

BUG=b:120686750
TEST=journalctl shows log output
TEST=/var/log/messages is still populated

Change-Id: I3539d107dc19ddf4a4928e237738a66846b33545
Reviewed-on: https://chromium-review.googlesource.com/1368816
Commit-Ready: Christopher Morin <cmtm@google.com>
Tested-by: Christopher Morin <cmtm@google.com>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Ereth McKnight-MacNeil <ereth@chromium.org>
diff --git a/common.sh b/common.sh
index f2e0009..ecc83e6 100644
--- a/common.sh
+++ b/common.sh
@@ -510,8 +510,8 @@
 
 # Mask for images without systemd.
 SYSTEMD_INSTALL_MASK="
-  /lib/systemd
-  /usr/lib/systemd
+  /lib/systemd/network
+  /usr/lib/systemd/system
 "
 
 # -----------------------------------------------------------------------------