virttest.utils_libguestfs: Add virt-inspector function.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
virttest.utils_test: Add test method for utils_test.libguestfs.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libguestfs.tests: Add test module for virt_inspect_operations.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>