qemu: Update to 2.5.1.1 [fixes CVE-2015-8558, CVE-2016-{3710, 3712}]

[Leo Famulari]

On Tue, May 10, 2016 at 07:35:44AM +0000, Leo Famulari wrote:
> lfam pushed a commit to branch master
> in repository guix.
> 
> commit b6449e61262374581b342aa4920bd37f2292923e
> Author: Leo Famulari <address@hidden>
> Date:   Mon May 9 20:48:36 2016 -0400
> 
>     gnu: qemu: Update to 2.5.1.1 [fixes CVE-2015-8558, CVE-2016-{3710, 3712}].
>     
>     * gnu/packages/qemu.scm (qemu): Update to 2.5.1.1.
>     [arguments]: Disable parallel tests.

QEMU has released 2.5.1.1 [0], which fixes these bugs:

* CVE-2015-8558
* CVE-2016-3710
* CVE-2016-3712
* an out of bounds write in 'cadence_uart' [1] 

I wasn't able to build it reliably on my x86_64 machine. Sometimes, it
would fail the test suite, and sometimes it would pass. It passed the
tests more reliably (--rounds=10) when parallel-tests are #f, so I made
that change.

[0]
https://lists.nongnu.org/archive/html/qemu-stable/2016-05/msg00008.html

[1]
http://git.qemu.org/?p=qemu.git;a=commit;h=5b7236f7256974d9c0286fa4837aa5e15ef5c629