lncli: allow unlock with password from stdin

[guggero]

As discussed with @lispmeister, this is needed to unlock lnd in a containerized environment like Kubernetes. Without this fix, additional unlocking software is needed that performs the unlock call through gRPC.

This could perhaps also be an acceptable compromise to what was suggested in #899.

[Roasbeef]

LGTM ⛷

[cfromknecht]

LGTM 🔑

[githorray]

Trouble building on Windows. go version go1.14 windows/amd64

cmd\lncli\commands.go:1810:34: cannot use syscall.Stdin (type syscall.Handle) as
 type int in argument to terminal.ReadPassword
Makefile:91: recipe for target 'build' failed
make: *** [build] Error 2

[githorray]

pw, err = terminal.ReadPassword(int(syscall.Stdin))

seems to have fixed it.

[guggero]

Thanks for reporting this, @githorray! Fix is up: #4069.

[githorray]

working great! thanks.