Make it possible to disable fuzz testing

These tests take a very long time on some platforms, and arent't
always strictly necessary.  This makes it possible to turn them
off.  The necessary binaries are still built, though, in case
someone still wants to do a manual run.

Reviewed-by: Andy Polyakov <appro@openssl.org>

Configure

@@ -342,6 +342,7 @@ my @disablables = (
     "filenames",
     "fuzz-libfuzzer",
     "fuzz-afl",
+    "fuzz-test",
     "gost",
     "heartbeats",
     "hw(-.+)?",

test/recipes/05-test_fuzz.t

@@ -15,6 +15,9 @@ use OpenSSL::Test::Utils;
 
 setup("test_fuzz");
 
+plan skip_all => "Fuzz testing is disabled by this OpenSSL build"
+    if disabled("fuzz-test");
+
 my @fuzzers = ('asn1', 'asn1parse', 'bignum', 'bndiv', 'conf', 'crl', 'server', 'x509');
 if (!disabled("cms")) {
     push @fuzzers, 'cms';