sky: Initialize energest as early as possible

If energest is initialized too late, the radio is not accounted
until the first switch. This is a problem when the radio is always
listening.
Support running multiple random seeds in case one fails
Only fail on real fails
Merge pull request #810 from cmorty/pull/sky_energest

sky: Initialize energest as early as possible / make regression testing more tolerant
packetbuf: Added function "packetbuf_holds_broadcast()" for checking whether the current packet is a
broadcast
packetbuf: Use packetbuf_holds_broadcast() all-over
framer: Added length function to contikimac-framer.c
framer: Some comments
framer-802154: create without frame802154.c
framer-802154: parse without frame802154.c
nullrdc: removed dependency on frame802154.c
node-id: Functions for extra configuration data
llsec: Allow for sharing PRNG
llsec: Compromise-resilient 802.15.4 security
apkes: Avoid nonce reuse in HELLOACKs, send authenticated short address
in ACKs
node-id: Function for appending extra config data
apkes: Fully pairwise keys scheme
apkes: Schedule erasure of master key within leap.c (better cohesion)
apkes: Trickle-based broadcasting of HELLOs
apkes: Automatic removal of disappeared neighbors