Set timeout threshold for alibaba ecs identification to avoid hanging.

On Alibaba ECS/EBM, virt-what used to run this tricky shell command:
```
( { echo -e "GET /latest/meta-datainstance/instance-type HTTP/1.0\r\nHost: 100.100.100.200\r\n\r" >&3; grep -sq 'ebm' <&3 ; } 3<> /dev/tcp/100.100.100.200/80 ) 2>/dev/null
```
which means the host fetches metadata and identifies its flavor.

However, the remote server '100.100.100.200' is accessible only within
Alibaba Cloud network, which keeps those hosts, not in that condition
mentioned above, hanging until syscall 'connect' timeout and get interrupted
by kernel, or even worse, hanging forever.

This commit set 1 second timeout at most for meta-data fetching process
to avoid that kind of hanging.

Signed-off-by: Weisson <hanxiaobupt@bupt.cn>