tests/acceptance: refactor boot_linux_console test to allow code reuse

tests/acceptance: refactor boot_linux_console test to allow code reuse

This patch splits code in BootLinuxConsole class into two different
classes to allow reusing it by record/replay tests.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <159073588490.20809.13942096070255577558.stgit@pasha-ThinkPad-X280>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
(cherry picked from commit 12121c496fcc609e23033c4a36399b54f98bcd56)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>