Acceptance tests: Add interrupt_interactive_console_until_pattern()

Acceptance tests: Add interrupt_interactive_console_until_pattern()

We need a function to interrupt interactive consoles.

Example: Interrupt U-Boot to set different environment values.

Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Tested-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Message-Id: <20200120235159.18510-4-f4bug@amsat.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>