oeqa: Streamline oe-selftest startup time

"bitbake -e" executions from get_bb_var calls are slow and slow down oe-selftest
startup. Rationalise the code to avoid them and minimise the number of "parsing"
locations we use by caching key variables and passing them around more.

This was particularly problematic with oe-selftest -j usage since it would
have multiple bitbake -e executions per process making parallel usage
particularly slow.

(From OE-Core rev: 3689cadeb07d76e66f97d890e844f899f69666fe)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/core/utils/concurrencytest.py

@@ -193,11 +193,12 @@ class dummybuf(object):
 #
 class ConcurrentTestSuite(unittest.TestSuite):
 
-    def __init__(self, suite, processes, setupfunc, removefunc):
+    def __init__(self, suite, processes, setupfunc, removefunc, bb_vars):
         super(ConcurrentTestSuite, self).__init__([suite])
         self.processes = processes
         self.setupfunc = setupfunc
         self.removefunc = removefunc
+        self.bb_vars = bb_vars
 
     def run(self, result):
         testservers, totaltests = fork_for_tests(self.processes, self)
@@ -243,7 +244,7 @@ class ConcurrentTestSuite(unittest.TestSuite):
 def fork_for_tests(concurrency_num, suite):
     testservers = []
     if 'BUILDDIR' in os.environ:
-        selftestdir = get_test_layer()
+        selftestdir = get_test_layer(suite.bb_vars['BBLAYERS'])
 
     test_blocks = partition_tests(suite, concurrency_num)
     # Clear the tests from the original suite so it doesn't keep them alive