automation: increase tests maximum time from 10s to 30s

automation: increase tests maximum time from 10s to 30s

10s is too low for the clang tests, this is the output from a clang
test:

  (XEN) [    6.512748] ***************************************************
  (XEN) [    6.513323] SELFTEST FAILURE: CORRECT BEHAVIOR CANNOT BE GUARANTEED
  (XEN) [    6.513891] ***************************************************
  (XEN) [    6.514469] 3... 2... 1...
  (XEN) [    9.520011] *** Serial input to DOM0 (type 'CTRL-a' three times to switch input)
  (XEN) [    9.544319] Freed 488kB init memory
  --- Xen Test Framework ---
  Environment: HVM 32bit (PAE 3 levels)
  Hello World
  Test result: SUCCESS
  (XEN) [    9.610977] Hardware Dom0 halted: halting machine

As can be seen from the output above booting Xen and the XTF test
takes ~10s, without accounting for the time it takes for QEMU to
initialize.

Increase the timeout to 30s to be on the safe side.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wl@xen.org>
Release-acked-by: Juergen Gross <jgross@suse.com>