log error description for DNS lookup failures

[Snawoot]

Logg error description to debug pretty common case of DNS failures which manifests like this:

#  sudo journalctl -fu mysterium-node.service
-- Logs begin at Sat 2020-09-26 04:31:05 UTC. --
Oct 03 20:04:04 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:04:04.973 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:05:38 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:05:38.286 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:06:10 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:06:10.371 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:06:42 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:06:42.458 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:07:14 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:07:14.573 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:08:18 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:08:18.862 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:08:50 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:08:50.942 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:10:25 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:10:25.557 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:10:57 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:10:57.658 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network
Oct 03 20:12:32 ca11.mysterium.pulseservers.com myst[1154]: 2021-10-03T20:12:32.433 WRN requests/dialer_swarm.go:288             > Failed to lookup host: testnet3-pilvytis.mysterium.network

[codecov-commenter]

Codecov Report

Merging #4022 (b054224) into master (a22793f) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4022      +/-   ##
==========================================
- Coverage   43.59%   43.48%   -0.11%     
==========================================
  Files         331      331              
  Lines       17457    17457              
==========================================
- Hits         7610     7591      -19     
- Misses       9087     9105      +18     
- Partials      760      761       +1     

Impacted Files	Coverage Δ
requests/dialer_swarm.go	77.09% <100.00%> (-3.06%)	⬇️
core/policy/oracle.go	86.48% <0.00%> (-5.41%)	⬇️
session/pingpong/invoice_tracker.go	62.76% <0.00%> (-2.41%)	⬇️
p2p/channel.go	73.49% <0.00%> (-2.13%)	⬇️
nat/traversal/pinger.go	79.84% <0.00%> (ø)
tequilapi/endpoints/sse_handler.go	71.32% <0.00%> (+2.20%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a22793f...b054224. Read the comment docs.