Failing test for long instance slug issue

This failing test demonstrates the long instance creation bug. The issue
is that because mongo will only allow database names < 64 characters long
the `hostName` storage selector fails when longer urls are used.
Add slug to database converter

This converts slugs that are longer than 63 characters so that the
underlying database name is 63 characters long. It does this by taking a
hash of the original slug, then appending it to a shortened version of
the slug.

This is necessary because of MongoDB's limit on the length of a database
name (which appears to be 64 characters, though the nodejs mongo module
only allows 63 characters).
Use slug to database converter for hostName storage

When the hostName storageSelector is being used the current hostname
determines the name of the database, previously overly long urls would
cause mongo errors, this commit uses the slug to database converter to
shorten any long urls so they can be consistently mapped to the
underlying database.
Merge branch 'handle-long-instance-slugs'