Fix collection of kernel crash into /var/spool/crash

Fix collection of kernel crash into /var/spool/crash

No kcrash was collected because the IsEnabled() test always failed:
we must do the kernel_collector->Enable() first.  I've not checked
if this might break the Override path (for local testing): it's more
important for the feature to work for real than in an artificial test.

BUG=837, 5865
TEST=logging_KernelCrashServer or manual procedure

Signed-off-by: Hugh Dickins <hughd@chromium.org>;

[kmixter1, 2010-09-09 03:29:07]

LGTM provided it now passes logging_KernelCrash.  I remember refactoring this
and I thought I ran KernelCrash but must not have.

[hughd, 2010-09-09 03:37:43]

Indeed it does now pass logging_KernelCrash: I just re-ran it to check,
Total PASS: 4/4 (100%)