oeqa/sdk: use bash to execute SDK test commands

oeqa/sdk: use bash to execute SDK test commands

The commands only work with with bash. If /bin/sh is
dash like in Debian, the command execution fails with
errors like:

Standard Output: /bin/sh: 5: export: --sysroot: bad variable name

and all SDK tests fail.

Signed-off-by: Mikko Rapeli <mikko.rapeli@bmw.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>