net.ftp: make ftp's tests just compile (not run) on CI

vlib/net/ftp/ftp_test.v

@@ -2,31 +2,36 @@ module main
 
 import net.ftp
 
-fn test_all() {
+fn test_ftp_client() {
+	make_client_connection()
+	assert true
+}
+
+// NB: this function makes network calls to external servers,
+// that is why it is not a very good idea to run it in CI.
+// If you want to run it manually, use `v -d network vlib/net/ftp/ftp_test.v`
+[if network]
+fn make_client_connection() {
 	mut ftp := ftp.new()
 	defer {
 		ftp.close()
 	}
-
 	assert ftp.connect('ftp.redhat.com')
-	assert ftp.login('ftp','ftp')
-
+	assert ftp.login('ftp', 'ftp')
 	pwd := ftp.pwd()
-
+	assert pwd.len > 0
 	ftp.cd('/')
 	dir_list1 := ftp.dir() or {
 		assert false
 		return
 	}
 	assert dir_list1.len > 0
-
 	ftp.cd('/suse/linux/enterprise/11Server/en/SAT-TOOLS/SRPMS/')
 	dir_list2 := ftp.dir() or {
 		assert false
 		return
 	}
 	assert dir_list2.len > 0
-
 	blob := ftp.get('katello-host-tools-3.3.5-8.sles11_4sat.src.rpm') or {
 		assert false
 		return