[feature] Add "Connect under Reset" option

[Gamadril]

• Programmer/board type: e.g Stlink/v2-onboard
• Programmer firmware version: e.g STSW-LINK007 2.27.15
• Operating system: Mac OS X
• Stlink tools version and/or git commit hash: 1.3.1-9-gc04df7f
• Stlink commandline tool name: st-flash
• Target chip (and optional board): e.g STM32F030F4

SWCLK and SWDIO pins of my mcu are used and configured as output. That means to program the flash I have to use the "Connect Under Reset" option. This option seems to be missing. At least adding --reset does not help in that case.

[xor-gate]

Connect under reset is not to difficult the stlink has a command to assert the nRST pin and then try to connect. But this needs to be implemented.

[iglooom]

I have a same trouble and use this workaround iglooom@19381ff
It is not fully "connect under reset", but working for me.

[xor-gate]

The nRST reset pin is assert differently. I'm not sure what the output state of the pin is in your commit. First we need to measure and then implement a fix which works for everybody.