move f_str_split() from UPF_Tests to Osmocom_VTY_Functions

I want to use it in a new function f_verify_talloc_bytes() added to
Osmocom_VTY_Functions.ttcn in I2948ee6f167369a2252f85b493e9653b93c7e4e9.

Change-Id: I9ddd9977734efd7599481261f04df82620845cef
2 files changed