Handle "--user current" and other valid users in the AccountManagerServiceShellCommand.

UserHandle.parseUserArg supports special params all and current.

See also: ag/9150276

bug: 139034865
Test: $ adb shell am get-current-user
10
$ adb shell cmd account set-bind-instant-service-allowed true
$ adb shell cmd account get-bind-instant-service-allowed
true
$ adb shell cmd account get-bind-instant-service-allowed --user 0
false
$ adb shell cmd account get-bind-instant-service-allowed --user 10
true
$ adb shell cmd account get-bind-instant-service-allowed --user current
true
$ adb shell cmd account set-bind-instant-service-allowed false
$ adb shell cmd account get-bind-instant-service-allowed --user 10
false
$ adb shell cmd account get-bind-instant-service-allowed --user current
false

Change-Id: I3a74aaa0dc83f8fb8b51225dfd33db184ddbde04