CHROMIUM: md: dm-verity fixed setting error_behavior

CHROMIUM: md: dm-verity fixed setting error_behavior

Need to be able to set the error behavior from either the device table
or from the linux command line.

The code only handled setting from the linux command line which
broke the platform_DMVetiryCorruption test. This was not noticed
earlier because of another bug in error handling that was just
recently was fixed which exposed this problem.

Now the code defaults to the command line but overrides from
the device table.

BUG=chromium:229621
TEST=platform_DMVerityCorruption
Signed-off-by: Paul Taysom <taysom@chromium.org>
Change-Id: I32a516deb2bd564b599e73177e479cddec789dfb
Reviewed-on: https://gerrit.chromium.org/gerrit/47744
Tested-by: Paul Taysom <taysom@chromium.org>
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>
Commit-Queue: Paul Taysom <taysom@chromium.org>