Enable cppcoreguidelines-init-variables

We try to enforce this rule, but clearly the robot can do a better job.
Enable the rule, and for init of all variables that clang-tidy finds in
error.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Icf64bc51b3180de29f7e92fa5c5f636e6b1462a6
diff --git a/.clang-tidy b/.clang-tidy
index 9c75d14..8932c14 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -187,6 +187,7 @@
 clang-analyzer-valist.ValistBase,
 clang-analyzer-webkit.NoUncountedMemberChecker,
 clang-analyzer-webkit.RefCntblBaseVirtualDtor,
+cppcoreguidelines-init-variables,
 misc-misplaced-const,
 misc-no-recursion,
 misc-redundant-expression,