Add module usability check script

firewalld/install_check.pl

@@ -0,0 +1,20 @@
+# install_check.pl
+
+use strict;
+use warnings;
+do 'firewalld-lib.pl';
+
+# is_installed(mode)
+# For mode 1, returns 2 if the server is installed and configured for use by
+# Webmin, 1 if installed but not configured, or 0 otherwise.
+# For mode 0, returns 1 if installed, 0 if not
+sub is_installed
+{
+my ($mode) = @_;
+return 0 if (&check_firewalld());
+if ($mode) {
+	return &is_firewalld_running() ? 2 : 1;
+	}
+return 1;
+}
+