ovs-lib: Wait for a longer time after SIGKILL.

ovs-lib: Wait for a longer time after SIGKILL.

Currently, when we stop a daemon, we first send it SIGTERM.
If SIGTERM did not work within ~5 seconds, we send a SIGKILL.
After sending SIGKILL, we wait only for 4 seconds, before giving
up.

If the system is extremely busy, there is a chance that a
process is not killed by the kernel within 4 seconds. In such
a case, when we try to start the daemon immediately, we see that
the pid inside the pid-file is valid and assume that the daemon
is still running. This leaves us in a state, where the daemon is
actually not running.

This patch increases the time waiting for the kernel to kill the
process to 60 seconds.

Bug #15404.
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>