1105278 - Corrects double UTC conversion issue for new RepoContentUnits

This fixes the timestamp problem with units of all types. The datetime was being converted to utc twice. This should resolve [BZ 1105278](https://bugzilla.redhat.com/show_bug.cgi?id=1105278).


I was able to reproduce timestamps using the existing code like:
```
> db.repo_content_units.find({repo_id: 'foo'})[0]
{
	"_id" : ObjectId("5398ba0754903459bdcad658"),
	"updated" : "2014-06-12T00:15:23Z",
	"repo_id" : "foo",
	"created" : "2014-06-12T00:15:23Z",
	"_ns" : "repo_content_units",
	"unit_id" : "fed3bef9-0066-41ba-865f-01eb582cdc4a",
	"unit_type_id" : "puppet_module",
	"owner_type" : "importer",
	"id" : "5398ba0754903459bdcad658",
	"owner_id" : "puppet_importer"
}
```

I was able to adjust the code, and it started saving them like this (which was the correct UTC time):

```
> db.repo_content_units.find({repo_id: 'foo'})[0]
{
	"_id" : ObjectId("5398ba0754903459bdcad658"),
	"updated" : "2014-06-11T20:20:23Z",
	"repo_id" : "foo",
	"created" : "2014-06-11T20:20:23Z",
	"_ns" : "repo_content_units",
	"unit_id" : "fed3bef9-0066-41ba-865f-01eb582cdc4a",
	"unit_type_id" : "puppet_module",
	"owner_type" : "importer",
	"id" : "5398ba0754903459bdcad658",
	"owner_id" : "puppet_importer"
}
```