condition: use 'selinux' rather than 'SELinux' as preferred spelling

The virtualization condition and others use lowercase identifiers, so
for the sake of keeping things least surprising, use lowercase
identifiers here too.

src/condition.c

@@ -134,7 +134,7 @@ static bool test_virtualization(const char *parameter) {
 
 static bool test_security(const char *parameter) {
 #ifdef HAVE_SELINUX
-        if (!strcasecmp(parameter, "SELinux"))
+        if (streq(parameter, "selinux"))
                 return is_selinux_enabled() > 0;
 #endif
         return false;