Changes

ttcn3-bts: Update cfg for test TC_tx_power_start_ramp_up_bcch

The test mentioned above is added in osmo-ttcn3-hacks.git
Ieb7444c6312bbeab64da2732393b3facf3e1f003.

config files are updated to make sense:
* "nominal power" in osmo-bsc.cfg reflects correct default nominal tx
  power of fake_trx.
* "osmotrx tx-attenuation" in osmo-bts.cfg is removed to let osmo-bts
  use the value received through OML (max_power_red 20).
* "power-ramp step-size" in osmo-bts.cfg is increased to speed up the
  test. There's no good reason to keep it lower.

Change-Id: I878d329dde3d2089ee3b68f56271fcb88d210025