test/py: test_efi_selftest.py: Updates for python 3 support

- In python 3 you must use raw strings for regex as other forms are
  deprecated and would require further changes to the pattern here.
  In one case this lets us have a simpler match pattern.
- As strings are now Unicode our complex tests (Euro symbol,
  SHIFT+ALT+FN 5) we need to declare that as a bytes string and then
  decode it for use.

Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Tom Rini <trini@konsulko.com>
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Changes in v2:
- New patch