tests: deduce test application name from folder

tests/Makefile.tests_common

-ifneq (,$(filter driver_%,$(APPLICATION)))
+APPLICATION ?= tests_$(notdir $(patsubst %/,%,$(CURDIR)))
+ifneq (,$(filter tests_driver_%,$(APPLICATION)))
     BOARD ?= samr21-xpro
 endif
 BOARD ?= native
 RIOTBASE ?= $(CURDIR)/../..
 QUIET ?= 1
-APPLICATION := tests_$(APPLICATION)