Change Http Client

[sumeetpatil]

This PR is raised to change the standard JDK HttpURLConnection to the Apache Http client. This is done to send keep-alive probes. Changing it to Apache Http Client enables users to configure keep-alive probes by changing OS parameters like net.inet.tcp.keepidle, net.inet.tcp.keepintvl and net.inet.tcp.keepcnt.

Working process of these OS params

1. The client opens a TCP Connection
2. If the connection is silent for net.inet.tcp.keepidle(tcp_keepalive_time) seconds, send a single empty ACK packet
3. Did the server respond with a corresponding ACK of its own?
   • YES - > Return to step 2
   • NO - > Wait net.inet.tcp.keepintvl(tcp_keepalive_intvl) seconds, then send another ACK. Repeat until the number of ACK probes that have been sent equals net.inet.tcp.keepcnt(tcp_keep_alive_probes). If no response has been received at this point, send a RST and terminate the connection.

Basic testing with vulas:app is done. I also tested 503 scenarios where we do retries.
I am testing more scenarios, meanwhile, you can review the code.

• Tests
• Documentation