red_worker: decrease the timeout when flushing commands and waiting for the client.
red_worker: decrease the timeout when flushing commands and waiting for the client.

150 seconds is way too long period for holding the guest driver and
waiting for a response for the client. This timeout was 15 seconds, but
when off-screen surfaces ware introduced it was arbitrarily multiplied by
10.
Other existing related bugs emphasize why it is important to decrease
the timeout:
(1) 994211 - the qxl driver waits for an async-io reponse for 60 seconds
    and after that, it switches to sync-io mode. Not only that the
    driver might use invalid data (since it didn't wait for the query to
    complete), falling back to sync-io mode introduces other errors.
(2) 994175 - spice server sometimes doesn't recognize that the client
             has disconnected.
(3) There might be cache inconsistency between the client and the server,
and then the display channel waits indefinitely for a cache item (e.g., bug
977998)

This patch changes the timeout to 30 seconds. I tested it under wifi +emulating 2.5Mbps network,
together with playing video on the guest and changing resolutions in a loop. The timeout didn't expired
during my tests.

This bug is related to rhbz#964136 (but from rhbz#964136 info it is still not
clear why the client wasn't responsive).

fgouget/spice,fgouget/spice,fgouget/spice,ya-mouse/spice,alon/spice-server,Fantu/spice,SPICE/spice,Fantu/spice,SPICE/spice,alon/spice-server,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice,elmarco/spice,elmarco/spice,alon/spice-server,Fantu/spice,ya-mouse/spice,elmarco/spice,ya-mouse/spice,Fantu/spice,elmarco/spice,fgouget/spice,alon/spice-server,elmarco/spice,alon/spice-server,freedesktop-unofficial-mirror/spice__spice,SPICE/spice,freedesktop-unofficial-mirror/spice__spice,freedesktop-unofficial-mirror/spice__spice