bts: Add paging related tests

We're testing at 80% and 200% of PCH capacity, both for either IMSI-only
or TMSI-only paging requests.  The way how we test ensures:

* the expected number of paged mobile identities end up on the Um interface
* we implicitly check the queuing limit of 200 paging records by
  overflowing it in the 20-seconds-of-200%-load cases
* we implicitly check the batching of mobile identities into different
  paging types
* we test the PCH load reporting over RSL

As a side note, in case you were ever wondering what's the expected
paging throughput / capacity, there are now helper functions to compute
it.  For our combined CCCH/SDCCH4, it's about 16 IMSIs per second or
about 32 TMSIs per second.

Change-Id: I0b80b72bdab3d80d915296d70e1174623fbd8610
6 files changed