Qualify drive label selector to drive tree...return the drive icon to the Cloud Import drop down.

A small grab bag of changes relating to cloud-import  icons/details panel:

1) Qualify drive label selector in test_util.js to just elements under the drive tree. And (re-)add the drive icon to the Cloud Import drop down.

2) Don't auto-hide cloud-import buttons when disabled...(fyi, they're disabled when in scanning and importing modes...we want the user to see them).

3) Format values on details panel in a human friendly way.

BUG=420680
TEST=browser_test: *FileManager*

Committed: https://crrev.com/fe2e3e76fe7842c9cdcf5c3aaa62081a564c42a2
Cr-Commit-Position: refs/heads/master@{#315309}

[Steve McKay, 2015-02-06 23:26:46]

Don't auto-hide cloud-import buttons when disabled.

[Steve McKay, 2015-02-06 23:30:21]

smckay@chromium.org changed reviewers:
+ fukino@chromium.org

[Steve McKay, 2015-02-07 00:13:17]

Format numbers and bytes in human friendly ways.

[fukino, 2015-02-09 04:31:52]

lgtm. Thanks!

[Steve McKay, 2015-02-09 15:24:49]

The CQ bit was checked by smckay@chromium.org

[commit-bot: I haz the power, 2015-02-09 15:25:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/902253003/40001

[commit-bot: I haz the power, 2015-02-09 15:59:02]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-02-09 15:59:26]

Patchset 3 (id:??) landed as
https://crrev.com/fe2e3e76fe7842c9cdcf5c3aaa62081a564c42a2
Cr-Commit-Position: refs/heads/master@{#315309}