Adding baud rate setting to TLS and UDP echo burst tests

[mirelachirica]

Description (required)

Baud rate setting added to TLS tests and UDP echo burst tests.

Summary of change (What the change is for and why)

UDP echo burst tests are failing and TLS tests get stuck when run for WISE_1570 with baud rate 9600 but are fine with 115200 baud rate.
The changes allow the needed baud rate to be configured.

Pull request type (required)

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 5 of 5 test jobs passed
Build number : 1
Build artifacts