Fix command line argument parsing in main.

Command line arguments are parsed twice in Scylla: once in main and once in Seastar's app_template::run.
The first parse is there to check if the "--version" flag is present --- in this case the version is printed
and the program exists.  The second parsing is correct; however, most of the arguments were improperly treated
as positional arguments during the first parsing (e.g., "--network host" would treat "host" as a positional argument).
This happened because the arguments weren't known to the command line parser.
This commit fixes the issue by moving the parsing code until after the arguments are registered.
Resolves #4141.

Signed-off-by: Kamil Braun <kbraun@scylladb.com>
(cherry picked from commit f155a2d)

main.cc

@@ -302,15 +302,7 @@ int main(int ac, char** av) {
     auto cfg = make_lw_shared<db::config>(ext);
     auto init = app.get_options_description().add_options();
 
-    // If --version is requested, print it out and exit immediately to avoid
-    // Seastar-specific warnings that may occur when running the app
     init("version", bpo::bool_switch(), "print version number and exit");
-    bpo::variables_map vm;
-    bpo::store(bpo::command_line_parser(ac, av).options(app.get_options_description()).allow_unregistered().run(), vm);
-    if (vm["version"].as<bool>()) {
-        print("%s\n", scylla_version());
-        return 0;
-    }
 
     bpo::options_description deprecated("Deprecated options - ignored");
     deprecated.add_options()
@@ -324,6 +316,15 @@ int main(int ac, char** av) {
     configurable::append_all(*cfg, init);
     cfg->add_options(init);
 
+    // If --version is requested, print it out and exit immediately to avoid
+    // Seastar-specific warnings that may occur when running the app
+    bpo::variables_map vm;
+    bpo::store(bpo::command_line_parser(ac, av).options(app.get_options_description()).allow_unregistered().run(), vm);
+    if (vm["version"].as<bool>()) {
+        print("%s\n", scylla_version());
+        return 0;
+    }
+
     distributed<database> db;
     seastar::sharded<service::cache_hitrate_calculator> cf_cache_hitrate_calculator;
     debug::db = &db;