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/runtime-test.py

@@ -193,8 +193,6 @@ postinst-delayed-t \
                            present on rootfs dir.
                         4. Boot the image created on qemu and verify that the file
                            created by postinst_boot recipe is present on image.
-                        5. Clean the packages and image created to test with
-                           different package managers
         Expected:       The files are successfully created during rootfs and boot
                         time for 3 different package managers: rpm,ipk,deb and
                         for initialization managers: sysvinit and systemd.
@@ -237,7 +235,3 @@ postinst-delayed-t \
                     sshargs = '-o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no'
                     result = runCmd('ssh %s root@%s %s' % (sshargs, qemu.ip, testcommand))
                     self.assertEqual(result.status, 0, 'File %s was not created at firts boot'% fileboot_name)
-
-                #Step 5
-                bitbake(' %s %s -c cleanall' % (rootfs_pkg, boot_pkg))
-                bitbake('core-image-minimal -c cleanall')