stable gas price estimate & clean up contract creation error handling

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #941 (f4b3441) into master (72c17b9) will increase coverage by 0.00%.
The diff coverage is 53.52%.

@@           Coverage Diff           @@
##           master     #941   +/-   ##
=======================================
  Coverage   49.03%   49.03%           
=======================================
  Files         422      422           
  Lines       47252    47257    +5     
=======================================
+ Hits        23169    23172    +3     
  Misses      22062    22062           
- Partials     2021     2023    +2     

Impacted Files	Coverage Δ
core/vm/cvm.go	15.93% <0.00%> (+0.06%)	⬆️
ctxc/gasprice/gasprice.go	36.08% <30.55%> (-4.35%)	⬇️
core/rawdb/freezer_table.go	69.93% <87.09%> (+2.35%)	⬆️
accounts/keystore/key.go	58.82% <0.00%> (-2.36%)	⬇️
core/rawdb/chain_iterator.go	60.25% <0.00%> (-1.29%)	⬇️
p2p/simulations/network.go	57.57% <0.00%> (-0.87%)	⬇️
ctxc/filters/api.go	44.60% <0.00%> (-0.75%)	⬇️
ctxc/downloader/downloader.go	76.00% <0.00%> (-0.54%)	⬇️
p2p/server.go	65.09% <0.00%> (-0.43%)	⬇️
core/blockchain.go	23.73% <0.00%> (+0.17%)	⬆️
... and 5 more