DeviceUtils: Fix SU command for pre-M devices

DeviceUtils: Fix SU command for pre-M devices

su -c CMD <-- CMD needs quoting
su 0 CMD <-- CMD does not need quoting

Ran into this when md5sum.py was trying to update the binary on a kitkat device
and needed to rm -rf it first.

BUG=

[agrieve, 2015-09-11 15:38:16]

agrieve@chromium.org changed reviewers:
+ jbudorick@chromium.org

[jbudorick, 2015-09-11 15:40:38]

lgtm

Odd that we didn't hit this previously (or prior to
https://codereview.chromium.org/1317453004)

[agrieve, 2015-09-11 15:56:03]

On 2015/09/11 15:40:38, jbudorick wrote:
> lgtm
> 
> Odd that we didn't hit this previously (or prior to
> https://codereview.chromium.org/1317453004)

Yeah, somewhat wondering if it's just my device that is special.

[agrieve, 2015-09-11 15:56:16]

The CQ bit was checked by agrieve@chromium.org

[commit-bot: I haz the power, 2015-09-11 15:56:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335983002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335983002/1

[commit-bot: I haz the power, 2015-09-11 16:43:45]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-11 16:43:46]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[jbudorick, 2015-09-11 16:46:07]

On 2015/09/11 at 15:56:03, agrieve wrote:
> On 2015/09/11 15:40:38, jbudorick wrote:
> > lgtm
> > 
> > Odd that we didn't hit this previously (or prior to
> > https://codereview.chromium.org/1317453004)
> 
> Yeah, somewhat wondering if it's just my device that is special.

Given that failure mode in provision_devices.py, it certainly seems like it.

[agrieve, 2015-09-11 17:38:24]

The CQ bit was checked by agrieve@chromium.org

[commit-bot: I haz the power, 2015-09-11 17:38:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1335983002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1335983002/1

[jbudorick, 2015-09-11 17:40:19]

The CQ bit was unchecked by jbudorick@chromium.org

[jbudorick, 2015-09-11 17:41:17]

On 2015/09/11 at 17:40:19, jbudorick wrote:
> The CQ bit was unchecked by jbudorick@chromium.org

I took this out of the CQ because:
 - I don't think it'll pass, given the way it failed in the same way twice
 - Even if it does pass, I don't think it's something we want to land given the
failures that occurred.