Ping Solr Env.

1. GET https://opensolr.com/solr_manager/api/ping
2. Parameters:
   1. ​email - your opensolr registration email address
   2. api_key - your opensolr api_key
   3. ​hostname - the hostname of the server you wish to ping

3. Example: https://opensolr.com/solr_manager/api/ping_server?email=PLEASE_LOG_IN&
   api_key=PLEASE_LOG_IN&hostname=us.opensolr.com