arc: Simplify cloud dpc error code handling

1. use base::UmaHistogramEnumeration in arc_optin_uma instead of macro
2. simplify the code in arc_session_manager for working with cloud dpc error
3. rename OptInCancelReason enum value to PROVISIONING_FAILED to indicate all kinds of failures

BUG=b:62613791
TEST=deploy to dut, disable playstore, re-enable playstore, successfully
finish the authorization flow
TEST=deploy android to dut with forced cloud dpc failure, enable
playstore, verify uma histogram is present in chrome://histograms

Change-Id: I0ec29e65c68ecb71551e200d06f31e990553d57c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2399881


Reviewed-by: Yury Khmel <khmel@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Muhammad Hasan Khan <mhasank@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805642}