testing, issue #1948: Increase TestRunDetach timeout

In production deployments, we are still seen:

--- FAIL: TestRunDetach (5.11 seconds)
	commands_test.go:42: Waiting for CmdRun timed out
=== RUN TestAttachDetach
--- FAIL: TestAttachDetach (5.06 seconds)
	commands_test.go:42: Waiting for CmdAttach timed ou

http://docker-ci.dotcloud.com/builders/docker/builds/332/steps/shell/logs/stdio
thttp://docker-ci.dotcloud.com/builders/pullrequest/builds/619/steps/shell/logs/stdio