Read official-build and dev-mode from the system properties.

This patch determines whether we are running in "dev-mode" and whehter
this is an official build in the "ro.secure" and "ro.debuggable" system
properties.

To reduce excessive logging output, this patch moved the logging of
dev-mode and unofficial builds to the beginning of the program and logs
just once.

Bug: 24077521
Test: Deployed an -eng build, update_engine thinks it is in dev-mode and non-official build.

Change-Id: Ib44823cb27dec3d39e1736d982869742b8211a57
diff --git a/real_system_state.cc b/real_system_state.cc
index 34ac5ed..1d11090 100644
--- a/real_system_state.cc
+++ b/real_system_state.cc
@@ -48,6 +48,9 @@
     return false;
   }
 
+  LOG_IF(INFO, !hardware_->IsNormalBootMode()) << "Booted in dev mode.";
+  LOG_IF(INFO, !hardware_->IsOfficialBuild()) << "Booted non-official build.";
+
   if (!shill_proxy_.Init()) {
     LOG(ERROR) << "Failed to initialize shill proxy.";
     return false;