Fix google-explicit-constructor warnings in system/core.

* Declare explicit conversion constructors.
* Add NOLINT for implicit conversion constructors.
* Fix also some misaligned indendations.

Bug: 28341362
Change-Id: Idf911f35923b408d92285cc1a053f382ba08c63e
Test: build with clang-tidy
diff --git a/logd/FlushCommand.h b/logd/FlushCommand.h
index 9224773..7172d5f 100644
--- a/logd/FlushCommand.h
+++ b/logd/FlushCommand.h
@@ -35,7 +35,7 @@
     uint64_t mTimeout;
 
 public:
-    FlushCommand(LogReader &mReader,
+    explicit FlushCommand(LogReader &mReader,
                  bool nonBlock = false,
                  unsigned long tail = -1,
                  unsigned int logMask = -1,