Enable cppcoreguidelines-pro-type-vararg check

We only had one usage of printf in the code that was in violation of
this rule, so replace it with iostreams, and enable the check.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Ie62165b599a996f34893aa5a3f8d1f6e6cbaf903
diff --git a/src/CPUSensor.cpp b/src/CPUSensor.cpp
index 6154b6f..0fdb2f4 100644
--- a/src/CPUSensor.cpp
+++ b/src/CPUSensor.cpp
@@ -117,6 +117,8 @@
     if (readingStateGood())
     {
         inputDev.close();
+
+        // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg)
         int fd = open(path.c_str(), O_RDONLY);
         if (fd >= 0)
         {