oeqa: make it work for multiple users

There are failures when multiple users run oe-selftest on the same
host:

PermissionError: [Errno 13] Permission denied: '/tmp/oe-saved-
tests/201812250324_qemu'

This is because /tmp/oe-saved-tests was created by user A, while user B tries
to write data in it, then the error will happen. This patch can fix the
problem.

Move the dumped data to ${LOG_DIR}/runtime-hostdump/ rather than
/tmp/oe-saved-tests/ to fix the problem.

(From OE-Core rev: e219fe5329599cd6c3682f521eaee3852a2c8980)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/dump.py

@@ -12,7 +12,7 @@ class BaseDumper(object):
         self.cmds = []
         # Some testing doesn't inherit testimage, so it is needed
         # to set some defaults.
-        self.parent_dir = parent_dir or "/tmp/oe-saved-tests"
+        self.parent_dir = parent_dir
         dft_cmds = """  top -bn1
                         iostat -x -z -N -d -p ALL 20 2
                         ps -ef