bts-trx: Allow re-try without exit if POWERON fails in osmo-trx
bts-trx: Allow re-try without exit if POWERON fails in osmo-trx

If POWERON fails, announce to BSC that the TRX is not available, and
announce it as available as soon as POWERON success is received.

Related: OS#3692
Change-Id: Iaa8f497381038fd7f9f779a8211ebc6453837c65

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts