sim: Enable logging in simulator test cases

When running simulations as unit tests, use a workaround from
https://stackoverflow.com/questions/30177845/how-to-initialize-the-logger-for-integration-tests
to initialize the logging system.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/src/lib.rs b/sim/src/lib.rs
index fe2d52e..d42a7b7 100644
--- a/sim/src/lib.rs
+++ b/sim/src/lib.rs
@@ -21,6 +21,7 @@
 
 mod caps;
 mod tlv;
+pub mod testlog;
 
 use simflash::{Flash, SimFlash};
 use mcuboot_sys::{c, AreaDesc, FlashId};