Revert "[login_manager] Stop honoring test-image-specific request to change core_pattern"
Revert "[login_manager] Stop honoring test-image-specific request to change core_pattern"

This reverts commit 1f0d2035d553e68193fa58e9baeeb76ef527a3ec.

Adding back this chunk of script to redirect chrome coredumps in response
to a magic file.  We no longer create the file on test images, so autotests
will be able to see these cores directed through crash_reporter, but
devs can touch the file manually to get core dumps for work.

BUG=None
TEST=build a test image, crash chrome.  a crash_reporter line should appear in /var/log/messages.  Then touch /mnt/stateful_partition/etc/enable_chromium_coredumps and crash chrome again.  Now, you should get a core in /mnt/stateful_partition/var/coredumps/

Review URL: http://codereview.chromium.org/4107002

Change-Id: I6c12e277a84a03430e8f84e657c59b90d81c25df

joshfire/chromiumos-platform-login_manager,chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager,chadversary/chromiumos.platform.login_manager,joshfire/chromiumos-platform-login_manager,joshfire/chromiumos-platform-login_manager