CA-153127: Extend the timeout protection scope for master db connection

In existent implement with_timestamp is only used to restrict the time
we receive the response body. If the master never respond the HTTP
request we will hang for far more than 2 minutes. Extend the time
protection scope could make sure that situation would also be handled.

This seems to be a regression introduced by 37e8d356.

Signed-off-by: Kaifeng Zhu <kaifeng.zhu@citrix.com>
CA-153127: Start the master-connection watchdog once

Start the master-connection watchdog from slave before attempting to
communicate with master. And use double-checked locking to prevent
the watchdog from being created multiple times.

Signed-off-by: Kaifeng Zhu <kaifeng.zhu@citrix.com>