oeqa/bbtests: Fix race over DL_DIR and SSTATE_DIR
Running "-c cleanall" on shared DL_DIR and SSTATE_DIR is antisocial.
It leads to hard to debug races where we wonder why files disappear
and reappear from those directories.
Fix this by using a specific set of directories for these tests. This
avoids a long standing bug on the autobuilder where aspell and man
sources would disappear.
[YOCTO #6276]
(From OE-Core rev:
6b089c4a79dc3aae00c8a6e7ab0f6ba4b4b5f138)
(From OE-Core rev:
f1447c256e027553442cf507e217323f7868000c)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
