Update blockdaemon nginx config

When starting nginx with the standalone-dev-nginx.conf, with the
previous values in the blockdaemon config, nginx errors out with an
error such as:

    2021/09/16 11:52:29 [emerg] 126854#0: host not found in upstream "YOUR_SERVER-solana-01.bdnodes.net" in blockdaemon-virt-server-config.conf:64

Setting it to a variable delays the name resolution until a request
is made. This makes it much easier to get a test nginx proxy up
and running.

Author: Jeff Schroeder

doc/nginx-configs/blockdaemon-virt-server-config.conf

@@ -16,29 +16,34 @@ server {
         try_files /nonexistent-used-for-try-testing @$http_upgrade;
     }
 
+    # These need to be manually edited to your specific config.
+    set $upstream_host YOUR_SERVER;
+    set $auth_token REPLACE_ME_WITH_YOUR_AUTH_TOKEN;
+
     location @websocket {
         # Cheat a little to make sure we don't have a trailing slash on the
         # path or we get a 405 response (method not allowed)
-        proxy_pass https://YOUR_SERVER-solana-01.bdnodes.net/$http_upgrade;
+        proxy_pass https://$upstream_host/$http_upgrade;
         proxy_http_version 1.1;
         proxy_set_header Host $proxy_host;
         # websocket requirements
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection "Upgrade";
         # Blockdaemon specific authentication requirement
-        proxy_set_header Authorization "Bearer REPLACE_ME_WITH_YOUR_AUTH_TOKEN";
+        proxy_set_header Authorization "Bearer $auth_token";
         proxy_redirect https://$proxy_host http://$server_name:$server_port;
         proxy_redirect https:// http://;
     }
 
     location @ {
-        proxy_pass https://YOUR_SERVER-solana-01.bdnodes.net$request_uri;
+        # Example: companyname-solana-09.bdnodes.net
+        proxy_pass https://$upstream_host$request_uri;
         proxy_http_version 1.1;
         proxy_set_header Host $proxy_host;
         # HTTP v.1.1 keepalive requirements
         proxy_set_header Connection "";
         # Blockdaemon specific authentication requirement
-        proxy_set_header Authorization "Bearer REPLACE_ME_WITH_YOUR_AUTH_TOKEN";
+        proxy_set_header Authorization "Bearer $auth_token";
         proxy_redirect https://$proxy_host http://$server_name:$server_port;
         proxy_redirect https:// http://;
     }
@@ -53,15 +58,18 @@ server {
 server {
     listen 7800;
 
+    set $upstream_host YOUR_SERVER;
+    set $auth_token REPLACE_ME_WITH_YOUR_AUTH_TOKEN;
+
     location / {
-        proxy_pass https://YOUR_SERVER-solana-01.bdnodes.net/websocket;
+        proxy_pass https://$upstream_host/websocket;
         proxy_http_version 1.1;
         proxy_set_header Host $proxy_host;
         # websocket requirements
         proxy_set_header Upgrade $http_upgrade;
         proxy_set_header Connection "Upgrade";
         # Blockdaemon specific authentication requirement
-        proxy_set_header Authorization "Bearer REPLACE_ME_WITH_YOUR_AUTH_TOKEN";
+        proxy_set_header Authorization "Bearer $auth_token";
         proxy_redirect https://$proxy_host http://$server_name:$server_port;
         proxy_redirect https:// http://;
     }