Add the log of starting idmap2d back

When IdmapDaemon calls kernel to start idmap2d, there is some unknown
exception happened. And, we need the exception log back to triage the
root cause well.

Bug: 232351707

Test: atest OverlayHostTests OverlayDeviceTests OverlayRemountedTest

Change-Id: I0fe533061c1ed4db03156cd4a055e8611611026a