automatically inherit VRF from pool in nipapd

When allocating from a pool, nipapd now looks at the implied VRF of a
pool and sets the same VRF to the new prefix being allocated. It doesn't
work for from-prefix operations as the input argument to from-prefix is
a list of prefixes and not a list of IDs of prefixes, so they can only
be uniquely identified by being specified in combination with a VRF.

Part of #286
automatically inherit VRF from pool in nipapd

When allocating from a pool, nipapd now looks at the implied VRF of a
pool and sets the same VRF to the new prefix being allocated. It doesn't
work for from-prefix operations as the input argument to from-prefix is
a list of prefixes and not a list of IDs of prefixes, so they can only
be uniquely identified by being specified in combination with a VRF.

Part of #286
Fix VRF lookup

Part of #286 and #295
Merge branch 'cli-from-pool-set-vrf' of github.com:plajjan/NIPAP into cli-from-pool-set-vrf

Conflicts:
	nipap/nipap/nipap.py
Merge pull request #295 from plajjan/cli-from-pool-set-vrf

automatically inherit VRF from pool in nipapd