env_dpdk/pci: ignore rte_bus_scan() errors

Extensive testing showed it can fail:
> EAL: eal_parse_sysfs_value(): cannot open sysfs value
> /sys/bus/pci/devices/0000:02:00.0/vendor
> EAL: Scan for (pci) bus failed.

spdk_pci_enumerate() would previously return with error because
of this and e.g. the test nvme hotplug app could immediately exit
with failure. A mis-timed scan shouldn't cause this kind of failure,
so ignore it's return code. This shouldn't cause any issues.

Change-Id: I9253219c218981a747774a8632335963cfb0db53
Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/2941


Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by:  <dongx.yi@intel.com>
Reviewed-by: Paul Luse <paul.e.luse@intel.com>
Reviewed-by: Michael Haeuptle <michaelhaeuptle@gmail.com>