Add -q (quiet) option to dnssec-signzone and dnssec-verify tool

With the move of the normal output to stdout, we need a way how to silence the
extra output, so the signed file name can be captured in a simple way.  This
commit adds `-q` command line option that will silence all the normal output
that get's printed from both tools.

bin/dnssec/dnssectool.c

@@ -57,7 +57,8 @@
 
 #include "dnssectool.h"
 
-int verbose;
+int verbose = 0;
+bool quiet = false;
 uint8_t dtype[8];
 
 static fatalcallback_t *fatalcallback = NULL;