test/py: Fix race conditions on EFI capsule tests

test/py: Fix race conditions on EFI capsule tests

efi_capsule_data() is called in each of the EFI tests to create and
setup the files we need. However, it also recreates the spi.bin file
that holds the SPI flash contents we rely on for the test validation.

This leads to weird errors since reading from the flash returns 0,
instead of the expected value if the file has been recreated.

Always restart our sandbox instance if the files are recreated.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>