THREESCALE-7941: Review warning displayed in apicast logs about variables_hash_max_size & variables_hash_bucket_size

 Increasing the limit of [variables_hash_bucket_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#variables_hash_bucket_size) make the warning message disapear.

 This message is a warning that NGiNX display when the used variables
 didn't fit the buffer. Increasing will also increase performance and
 will not show this warning.

 The NGiNX documenation about hashes says:

 ```
 To quickly process static sets of data such as server names, map
 directive’s values, MIME types, names of request header strings, nginx
 uses hash tables. During the start and each re-configuration nginx
 selects the minimum possible sizes of hash tables such that the bucket
 size that stores keys with identical hash values does not exceed the
 configured parameter (hash bucket size). The size of a table is
 expressed in buckets. The adjustment is continued until the table size
 exceeds the hash max size parameter. Most hashes have the corresponding
 directives that allow changing these parameters, for example, for the
 server names hash they are server_names_hash_max_size and
 server_names_hash_bucket_size.

 The hash bucket size parameter is aligned to the size that is a multiple
 of the processor’s cache line size. This speeds up key search in a hash
 on modern processors by reducing the number of memory accesses. If hash
 bucket size is equal to one processor’s cache line size then the number
 of memory accesses during the key search will be two in the worst case —
 first to compute the bucket address, and second during the key search
 inside the bucket. Therefore, if nginx emits the message requesting to
 increase either hash max size or hash bucket size then the first
 parameter should first be increased.
 ```
 Reference: [NGiNX: Setting up hashes](http://nginx.org/en/docs/hash.html)

 Also, to check the processor's cache line size, use:

 `cat /sys/devices/system/cpu/cpu*/cache/index*/coherency_line_size | head -n 1`

 Source: [https://stackoverflow.com/questions/794632/programmatically-get-the-cache-line-size]

 This commit fix the Jira issue THREESCALE-7941.

 [https://issues.redhat.com/browse/THREESCALE-7941]

Author: ernaniaz

gateway/conf/nginx.conf.liquid

@@ -43,7 +43,8 @@ http {
   tcp_nodelay        on;
   server_tokens off;
 
-
+  variables_hash_bucket_size 128;
+  variables_hash_max_size 1024;
 
   proxy_cache_path /tmp/cache levels=1:2 keys_zone=apicast_cache:10m;
   # Enabling the Lua code cache is strongly encouraged for production use