test/py: Add support to enable check for bad pattern

Executing a u-boot command may raise an error or extra bad pattern,
beyond the default bad patterns. Providing a way to enable the console
output error check in test.

For example, description for OS boot test:
import re
check_type = 'kernel_boot_error'
check_pattern = re.compile('ERROR -2: can't get kernel image!')
with u_boot_console.enable_check(check_type, check_pattern):
    u_boot_console.run_command('<boot command>')

Signed-off-by: Love Kumar <love.kumar@amd.com>