Refactor mongodb connection

[lirantal]

This refactoring to mongodb connection handling will solve:

1. username or password with special chars like @ won't be handled correctly to connect to mongodb via the connection string uri, so this refactor solves that
2. exit on mongodb error instead of hang the nodejs app idle

[lirantal]

Example:

[lirantal]

@roieki @NeverOddOrEven what do you think?

[lirantal]

@Shrizzy @amoshaviv care to take a review here? it looks like a much needed change IMHO and I want to merge

[ilanbiala]

Why so many process URIs? In my opinion, let the user change the one included if necessary, but no need to include one for every database service.

[ilanbiala]

@lirantal other than the couple comments that I put, LGTM. The nice printout is definitely more useful, but all the process.env stuff and the options IMO is unnecessary.

[lirantal]

@ilanbiala thanks for reviewing, couple of comments:

1. As you can see, I didn't introduce the several environment variable URI variations, they were there before, and if someone cared to approve it then probably for a reason. I do agree with you that it may be 'too magicful' trying to resolve the URI like that but that can be solved in another, more concise PR for that.
2. The user/pass can't be specified in the URI if they include special characters like !@#$%^&* - that's one of the reasons why I refactored the db connection like that (it's a known problem/bug with mongoose URI parameter)

[NeverOddOrEven]

I just went over this for what it's worth. I like this change a lot!

[lirantal]

@NeverOddOrEven glad you liked it :)