add some unit tests for class registry.RegistryServer

tests/dh2048.pem

+-----BEGIN DH PARAMETERS-----
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+BnUtiqlB3IlGCg6RWXRGcdEZ50blLQZ0kwIBAg==
+-----END DH PARAMETERS-----

tests/registry.json

+{
+    "verbose": 1, 
+    "ca": "root.crt", 
+    "port": 9090, 
+    "anonymous_prefix_length": null, 
+    "smtp_pwd": null, 
+    "client_count": 10, 
+    "authorized_origin": [
+        "127.0.0.1", 
+        "::1"
+    ], 
+    "bind6": "::", 
+    "ipv4": null, 
+    "prefix_length": 16, 
+    "min_protocol": 1, 
+    "smtp_starttls": false, 
+    "run": "/var/run/re6stnet", 
+    "bind4": "0.0.0.0", 
+    "dh": "dh2048.pem", 
+    "db": "registry.db", 
+    "mailhost": "miku@miku.com", 
+    "key": "registry.key", 
+    "encrypt": false, 
+    "logfile": "registry.log", 
+    "max_clients": null, 
+    "smtp_user": null, 
+    "same_country": null, 
+    "tunnel_refresh": 300, 
+    "hello": 15
+}
\ No newline at end of file

tests/registry.key

+-----BEGIN RSA PRIVATE KEY-----
+MIIEpQIBAAKCAQEA2yS7SlkxfMc8ydVbFPv8kZFQQp1dyda4Dt41P3+klO01TE0k
+JY25pvpBcYFz3tbADB/m6zJlvuA9eVTy7cxodioRaYiUCZjgUbXZ2/BziUIGygDL
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+avFFoiUUtviOdvqBketnWkIiwzL8lzjHOwjYvdRiGv9Fkoty0SKXbp8=
+-----END RSA PRIVATE KEY-----

tests/root.crt

+-----BEGIN CERTIFICATE-----
+MIID4jCCAsqgAwIBAgIHASABDbgAQjANBgkqhkiG9w0BAQsFADCBhjELMAkGA1UE
+BhMCRlIxDjAMBgNVBAgMBUxJTExFMQ4wDAYDVQQHDAVMSUxMRTEhMB8GA1UECgwY
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+-----END CERTIFICATE-----