accounts/keystore: prevent key-loading in geth account new

[holiman]

The changes introduced in #15171 made an initial scan of the filesystem performed upon startup. This had an adverse effect in the case where geth was not actually intended to run in normal 'daemon'-mode, but was only meant for brief geth account new.

This PR makes the geth account new not configure a complete full node, but instead initalize a keystore directly. When doing so, it can avoind to load all existing files from the keystore directory.

Fixes #15511.

On commit 88b1db728826efd499ea407579f41e8b683d6b53 (with 55k accounts):

#time yes | build/bin/geth --datadir ~/tmp/account_gen account  new
Your new account is locked with a password. Please give a password. Do not forget this password.
!! Unsupported terminal, password will be echoed.
Passphrase: 
Repeat passphrase: 
Address: {b3d522cbff4c47cfeee5252e29729b52ada68b3a}

real	0m46.971s
user	0m49.480s
sys	0m1.524s

With this PR:

#time yes | build/bin/geth --datadir ~/tmp/account_gen account  new
Your new account is locked with a password. Please give a password. Do not forget this password.
!! Unsupported terminal, password will be echoed.
Passphrase: 
Repeat passphrase: 
Address: {a9486ada158b8dc2e2008dbbc20351f81f7af95f}

real	0m0.743s
user	0m0.712s
sys	0m0.040s

[karalabe]

I'm not sure this is actually correct.

https://github.com/ethereum/go-ethereum/blob/master/node/config.go#L72

	// KeyStoreDir is the file system folder that contains private keys. The directory can
	// be specified as a relative path, in which case it is resolved relative to the
	// current directory.
	//
	// If KeyStoreDir is empty, the default location is the "keystore" subdirectory of
	// DataDir. If DataDir is unspecified and KeyStoreDir is empty, an ephemeral directory
	// is created by New and destroyed when the node is stopped.
	KeyStoreDir string `toml:",omitempty"`

I.e. The keystore path given as a flag, config or otherwise can be resolved to a lot of different locations. You PR essentially removes this resolution altogether.

[karalabe]

I think this is a very ugly API hack :P

[holiman]

@karalabe you were totally right. I pushed some changes, so that it now correctly uses the configuration. The code is on the level of 'it works but it aint pretty'. If I get the time, I'll try to make another stab at a nicer fix.

[holiman]

Closing this in favour of #15529