libvirt.tests: Fix explicitly reference /tmp to test.tmpdir.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libvirt.tests: Pass timeout instead of internal_timeout for session.

There is no need to set internal_timeout for "cat /proc/cpuinfo".
It will waste 10s for each case which calls it.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #513 from yumingfei/issue_90

libvirt.tests: Fix explicitly reference /tmp to test.tmpdir.