test: Store brief log per test and use as default report_stdout

Change-Id: I0972ba56a42c24f3d3b1bc94bcbdaca86026046a
diff --git a/src/osmo_gsm_tester/core/log.py b/src/osmo_gsm_tester/core/log.py
index f1954d1..b8182f5 100644
--- a/src/osmo_gsm_tester/core/log.py
+++ b/src/osmo_gsm_tester/core/log.py
@@ -46,6 +46,9 @@
 C_BUS = 'bus'
 C_DEFAULT = '---'
 
+FILE_LOG = 'log'
+FILE_LOG_BRIEF = 'log_brief'
+
 LOG_CTX_VAR = '_log_ctx_'
 
 def dbg(*messages, _origin=None, _category=None, _src=None, **named_items):