improve gas price suggestions in retry tx's

[frankiebee]

At this moment the gas price can be set to 0... which when retried the minimum can be set to 0 because 0 / 100 * 10 = 0 so lets not do this because txs will either fail or hang in pending.

I can do the background if you want to handle the ui @danjm

[tmashuang]

#4058
#4073
#4037

TLDR; private/test networks. Maybe just mainnet?

[danfinlay]

Rather than doing a blanket ban on a price that could be valid for many networks, I'd like to learn why 0 was estimated.

The retry issue would be solved with #5779.

[frankiebee]

@danfinlay 0 was not estimated for gasPrice the user chose it

[frankiebee]

and then was able to continue using it through the retries. The actual recommended gas price was ignored

[frankiebee]

i've renamed this issue to better reflect the problem