VNC harcoded server name removed

VNC server can be other than WebSockify, so there is a need to
  configure it once in a while for various deployments

    - added config option
    - updated test

Change-Id: I938bae347eaa9fcf76e4118188b325ba6d3efa77
Closes-Bug: #1748339

releasenotes/notes/vnc-hardcoded-server-name-removed-6f8d1e90a175dc08.yaml

@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    New string configuration option ``vnc_server_header`` is added
+    to ``compute-feature-enabled`` section. It offers to provide VNC server
+    name that is to be expected in the responce header. For example, obvious
+    at hand names is 'WebSockify', 'nginx'.
+fixes:
+  - |
+    Fix VNC server response header issue when it is behind reverse proxy

tempest/api/compute/servers/test_novnc.py

@@ -151,11 +151,22 @@ class NoVNCConsoleTestJSON(base.BaseV2ComputeTest):
         self.assertTrue(
             self._websocket.response.startswith(b'HTTP/1.1 101 Switching '
                                                 b'Protocols\r\n'),
-            'Did not get the expected 101 on the websockify call: '
-            + six.text_type(self._websocket.response))
-        self.assertTrue(
-            self._websocket.response.find(b'Server: WebSockify') > 0,
-            'Did not get the expected WebSocket HTTP Response.')
+            'Did not get the expected 101 on the {} call: {}'.format(
+                CONF.compute_feature_enabled.vnc_server_header,
+                six.text_type(self._websocket.response)
+            )
+        )
+        # Since every other server type returns Headers with different case
+        # (for example 'nginx'), lowercase must be applied to eliminate issues.
+        _desired_header = "server: {0}".format(
+            CONF.compute_feature_enabled.vnc_server_header
+        ).lower()
+        _response = six.text_type(self._websocket.response).lower()
+        self.assertIn(
+            _desired_header,
+            _response,
+            'Did not get the expected WebSocket HTTP Response.'
+        )
 
     @decorators.idempotent_id('c640fdff-8ab4-45a4-a5d8-7e6146cbd0dc')
     def test_novnc(self):

tempest/config.py

@@ -404,6 +404,10 @@ ComputeFeaturesGroup = [
                 default=False,
                 help='Enable VNC console. This configuration value should '
                      'be same as [nova.vnc]->vnc_enabled in nova.conf'),
+    cfg.StrOpt('vnc_server_header',
+               default='WebSockify',
+               help='Expected VNC server name (WebSockify, nginx, etc) '
+                    'in response header.'),
     cfg.BoolOpt('spice_console',
                 default=False,
                 help='Enable Spice console. This configuration value should '