Various cleanups of issues caught by clang-tidy

Change-Id: I6e79c121e7c9032cf5053dd31971e719fe76f4b6
diff --git a/aos/common/time.h b/aos/common/time.h
index 226cbc2..a176ba0 100644
--- a/aos/common/time.h
+++ b/aos/common/time.h
@@ -47,7 +47,7 @@
 
   static const Time kZero;
 
-  constexpr Time(int32_t sec = 0, int32_t nsec = 0)
+  explicit constexpr Time(int32_t sec = 0, int32_t nsec = 0)
       : sec_(sec), nsec_(CheckConstexpr(nsec)) {
   }
   #ifndef SWIG