oeqa/selftest: don't use cleanall in selftests

* devtool: oeqa.selftest.devtool.DevtoolTests is taking 4 or more hours on the
  autobuilder because the cleanall call deletes the tarball of the kernel
  source, forcing a large clone which is especially long on an NFS mount.

  The cleanall invocation isn't really required here and switching to clean
  instead should avoid hours of re-cloning the same repository each time we
  run oe-selftest on the autobuilder.
* buildoptions: We only need to ensure the first image isn't an incremental
  image, clean will suffice here.
* runtime-test: no need to clean up the artefacts generated during the test,
  let's leave that to a higher level process rather than using the cleanall
  hammer.

(From OE-Core rev: 9c948d3de08f158387e08a17cdc0cedc7d26bb54)

Signed-off-by: Joshua Lock <joshua.g.lock@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/devtool.py

@@ -1654,7 +1654,7 @@ class DevtoolTests(DevtoolBase):
 
         tmpconfig = os.path.join(buildir, '.config')
         #Step 3
-        bitbake('linux-yocto -c cleanall')
+        bitbake('linux-yocto -c clean')
         #Step 4.1
         runCmd('devtool modify virtual/kernel -x %s' % tempdir)
         self.assertTrue(os.path.exists(os.path.join(tempdir, 'Makefile')),