Long Post Query doesn't work with the external HTTP Solr server

[taojing2002]

When we use the post query to pass a long query to Metacat, Metacat will relay the query to Solr. It works well when we used the embedded Solr server. However, it doesn't work after the external Solr server was introduced. We got this error:

Solr server error: Error from server at http://localhost:8983/solr/metacat-index: Expected mime type application/octet-stream but got text/html. <h1>Bad Message 414</h1><pre>reason: URI Too Long</pre>

It seems the query is sent by the HTTP GET method to the Solr server. We need to use the POST method as well.

[taojing2002]

We specify the POST method when we use the mn post query to query solr. https://github.com/NCEAS/metacat/commit/57e11f0eec0a1241ba72ceaf0cb856e668aa506c