tests: bluetooth: tester: Make UART usage consistent

We use UART1 for UART pipe in a number of qemu tests, so lets do the
same thing for the bluetooth test and move the bluetooth uart to UART2.

Jira: ZEP-2412.

Signed-off-by: Savinay Dharmappa <savinay.dharmappa@intel.com>
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>