qemu.tests: update test script according test case

updated test script since case steps changed;

Signed-off-by: Xu Tian <xutian@redhat.com>
qemu.test: remove useless file

remove useless script block_stream_with_stress, since
block_stream_stress in used by block_stream.with_stress tests;

Signed-off-by: Xu Tian <xutian@redhat.com>
Merge pull request #723 from xutian/fix_block_stream

some fix for block stream tests