virttest.libvirt_vm: Add function to get libvirt job's type.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
shared.scripts: Add a tool for setting 0 to memory.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #1782 from yumingfei/migration_complementary

virttest.libvirt_vm: Add function to get job's type.