Create separate udev collector class

Previously added a udev collector to CrashCollector.  Now it's time to
put it in its own class.

BUG=chromium-os:30268
TEST=See "TEST=" under  https://gerrit.chromium.org/gerrit/21498

Change-Id: I6a62826cb84ef7ccd42a512b00e127af6de3280d
Signed-off-by: Simon Que <[email protected]>
Reviewed-on: https://gerrit.chromium.org/gerrit/25112
Reviewed-by: Michael Krebs <[email protected]>
8 files changed