[Telemetry] Cache updating apks.

[Telemetry] Cache updating apks.

This will both improve cycle time and reduce log spam. See:
http://build.chromium.org/p/chromium.linux/builders/Android%20Tests%20%28dbg%29/builds/20012/steps/telemetry_perf_unittests/logs/stdio

BUG=
NOTRY=True

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266054

[dtu, 2014-04-24 20:19:29]

lgtm

[dtu, 2014-04-24 20:19:30]

lgtm

lgtm

[dtu, 2014-04-24 20:19:30]

lgtm

lgtm

lgtm

[tonyg, 2014-04-24 20:19:55]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-04-24 21:46:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tonyg@chromium.org/257493002/1

[commit-bot: I haz the power, 2014-04-24 23:30:35]

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

[commit-bot: I haz the power, 2014-04-24 23:30:36]

Try jobs failed on following builders:
  tryserver.chromium on linux_chromium_chromeos_rel

[tonyg, 2014-04-24 23:37:28]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-04-24 23:39:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tonyg@chromium.org/257493002/1

[commit-bot: I haz the power, 2014-04-24 23:51:32]

Change committed as 266054