lntest+github: add flag temptest to run tests separately

This commit adds a new flag `temptest` so we can run new and old tests
separately. This flag will be removed once the migration from old tests
to new tests is finished.

make/testing_flags.mk

@@ -9,6 +9,11 @@ NUM_ITEST_TRANCHES = 4
 ITEST_PARALLELISM = $(NUM_ITEST_TRANCHES)
 POSTGRES_START_DELAY = 5
 
+# Build temp tests only. TODO(yy): remove.
+ifneq ($(temptest),)
+ITEST_FLAGS += -temptest=$(temptest)
+endif
+
 # If rpc option is set also add all extra RPC tags to DEV_TAGS
 ifneq ($(with-rpc),)
 DEV_TAGS += $(RPC_TAGS)