Adding reconnect option to tcollector.

Adding --reconnect-interval option (in seconds) that will rebind the TCP connection to the TSD server.
It's leveraging the verify_conn() function to trigger a TCP reconnection.
This is particularly useful if using a round-robin DNS or any kind of VIP.

Defaults to 0 (no reconnection)

Signed-off-by: Vasiliy Kiryanov <vasiliy.kiryanov@gmail.com>