pcu: Add VTY support and use it to set (M)CS lqual thresholds

Requires osmo-pcu.git I3430abb5fc622dec293457466e760de95fa3a05c, before
that commit OsmoPCU cmd prompt contained a dash which resulted in TTCN3
being unable to match it.

Change-Id: I221675721b65b3ab44179e9657da70ba4004d7de
4 files changed