sim: add bootstrap test

Add caps for bootstrap option and implement simple bootstrap test
for the simulator.

Signed-off-by: Fabio Utzig <fabio.utzig@nordicsemi.no>
diff --git a/boot/bootutil/src/caps.c b/boot/bootutil/src/caps.c
index 56b5791..a21bc09 100644
--- a/boot/bootutil/src/caps.c
+++ b/boot/bootutil/src/caps.c
@@ -65,6 +65,9 @@
 #if defined(MCUBOOT_DOWNGRADE_PREVENTION)
     res |= BOOTUTIL_CAP_DOWNGRADE_PREVENTION;
 #endif
+#if defined(MCUBOOT_BOOTSTRAP)
+    res |= BOOTUTIL_CAP_BOOTSTRAP;
+#endif
 
     return res;
 }