test: stabilize test_efi_secboot

When setting up the console via function efi_console_register() we call
query_console_serial(). This functions sends an escape sequence to the
terminal to query the display size. The response is another escape
sequence.

console.run_command_list() is looking for a regular expression '^==>'.
If the escape sequence for the screen size precedes the prompt without a
line break, no match is found.

When efi_disk_register() is called before efi_console_register() this leads
to a test failuere of the UEFI secure boot tests.

We can avoid the problem if the first UEFI command passed to
u_boot_console.run_command_list() produces output. This patch achieves this
by appending '; echo' to the first UEFI related command of the problematic
tests.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>