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/LogCommand.h b/logd/LogCommand.h
index c944478..0adc2a1 100644
--- a/logd/LogCommand.h
+++ b/logd/LogCommand.h
@@ -22,7 +22,7 @@
 
 class LogCommand : public FrameworkCommand {
 public:
-    LogCommand(const char *cmd);
+    explicit LogCommand(const char *cmd);
     virtual ~LogCommand() {}
 };