REGTEST: run-regtests: implement #REQUIRE_BINARIES

Implement #REQUIRE_BINARIES for vtc files.

The run-regtests.sh script will check if the binary is available in the
environment, if not, it wil disable the vtc.
diff --git a/reg-tests/ssl/set_ssl_cert.vtc b/reg-tests/ssl/set_ssl_cert.vtc
index 1cdbd42..9497be8 100644
--- a/reg-tests/ssl/set_ssl_cert.vtc
+++ b/reg-tests/ssl/set_ssl_cert.vtc
@@ -9,6 +9,7 @@
 
 varnishtest "Test the 'set ssl cert' feature of the CLI"
 #REQUIRE_OPTIONS=OPENSSL
+#REQUIRE_BINARIES=socat,curl
 feature ignore_unknown_macro