TS-2622: optimize the function ink_cluster_time

  1. remove useless two global variables
  2. use ink_get_hrtime() instead of time(NULL)
  3. remove useless CAS to set variable global_time
TS-2603: Do not update hostdb if intercept exists

We should not update hostdb if a HttpSM was intercepted, as the
HttpSM did not really connect to the origin server.  Otherwise we
may set the hostdb address to zero if timeout occurs.

Signed-off-by: Quehan <quehan@taobao.com>