oeqa/selftest/context: Replace deprecated imp module usage

Avoid the warning:

meta/lib/oeqa/selftest/context.py:8: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
  import imp

In this case importlib is a direct replacement.

(From OE-Core rev: db7a60c36a2d3eefc61ae6e1ede01680dc932035)

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

meta/lib/oeqa/selftest/context.py

@@ -5,7 +5,7 @@ import os
 import time
 import glob
 import sys
-import imp
+import importlib
 import signal
 from shutil import copyfile
 from random import choice
@@ -178,7 +178,7 @@ class OESelftestTestContextExecutor(OETestContextExecutor):
                     self.tc.logger.info("\t%s" % l)
 
                 sys.path.extend(layer_libdirs)
-                imp.reload(oeqa.selftest)
+                importlib.reload(oeqa.selftest)
 
         _check_required_env_variables(["BUILDDIR"])
         _check_presence_meta_selftest()