Let AutoConnectHandler wait for user policy before disconnecting

AutoConnectHandler didn't wait for user policy before disconnecting from
unmanaged network. This will lead to user policy not downloaded or
applied.

This commit make AutoConnectHandler to wait for user policy first before
disconnecting from unmanaged network if device policy requires to do so.

BUG=553497

Review URL: https://codereview.chromium.org/1415683013

Cr-Commit-Position: refs/heads/master@{#358730}
3 files changed