When idf_monitor is launched from make, it gets modified TEST_COMPONENTS
variable which contains full paths to the test components instead of the
names. This causes TEST_COMPONENT_PATHS to be empty and the unit test
app gets built without any test components.
This change introduces an internal TEST_COMPONENTS_LIST variable which
gets set either from $(COMPONENTS) if TESTS_ALL is 1, and from
TEST_COMOPONENTS otherwise.
Bootloader makefile is also fixed to avoid propagating TESTS_ALL to the
bootloader build step.