Decode URI in RequestManageCredentials

* URI should be human readable and not
  in percent-encoded form

Manual Testing steps
* Install TestDPC
* Select preference Request to manage credentials
* Verify activity displays URIs in a human
  readable format

Bug: 177900145
Test: Manual testing
Change-Id: I7b5f92f4939491a40bc3728aab56e06886fc08f1