Fixed bug [YOCTO #2052]. Added sanity check for variables of PRSERV_HOST
and PRSERV_PORT, also for the connection availabity of prservice.
(From OE-Core rev: 7588a4f2e2728da0ff7a773b18527f3711b138f2)
Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>