OAI: Solr Timezone Issue fix

Fixed timezone issue.

It still lacks of a proper test scenario to check if it's really ok, although I had reproduced the issue in my own development machine.

The next version of the OAI interface (pull request coming soon) fully covers this issue.
If I am right, using the Database will have no problem, it's a solr issue only, but I proved it in my dev machine only. 

Just to raise the confidence level, could anyone check for it?

**Jira**: https://jira.duraspace.org/browse/DS-1445