Calling stlink_reset() causes the target to reset after disconnecting.

While trying to read/write directly from/to RAM i noticed that the STM32 would always reset after stmlink disconnects.
This is not a good thing when using stlink to access RAM on running programs.

Unfortunately writing to Flash fails if this reset does not occur.

My hardware is STM32VLDISCOVER where this change works as intended
however i am not able to verify this patch on other platforms.