bts: Allow setting amount of TRX and timeslot in cfg and from test at runtime

The num_trx attribute for a given BTS states the number of TRX to be
used by that BTS. If more than num_trx are configured in trx_list in the
cfg file, then only up to num_trx are taken into account. If a num_trx
value higher than max_trx is specified throuygh config file or at
runtime by the test, an exception is raised explaining the issue.

The num/max_trx attributes are overlayed along the config levels
(generic -> bsc_bts -> specific bts-type -> specific resource object).
This way we can specify a long list of trx+timeslot config in the
generic config (bsc_bts), and tune for each model and specific BTS which
is the desired default number of TRX, as well as the maximum supported
per type.

Change-Id: I7f46eaf7a16f03268653299c93600c0443f691ac
4 files changed