qmp client: increase timeout for thaw

qmp client: increase timeout for thaw

Using a loop of freeze, sleep 5, thaw, sleep 5, an idling Windows 11
VM with 4 cores and 8GiB RAM once took 54 seconds for thawing. It took
less than a second about 90% of the time and maximum of a few seconds
for the majortiy of other cases, but there can be outliers where 10
seconds is not enough.

And there can be hookscripts executed upon thaw, which might also not
complete instantly.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>