find tables inside non-default schema when serving off a metadata

[llllllllll]

The name of a table include the schema prefix which would disallow us from finding a table in a metadata object if it was not the default schema. This goes with: blaze/odo#242

The '.',join is okay because that is what the key will look like when you have a dotted schema name:

In [2]: import sqlalchemy as sa

In [3]: ds = bz.Data(sa.MetaData('postgresql://localhost/test', schema='wow.this.sucks'))

In [4]: ds.data.tables
Out[4]: immutabledict({'wow.this.sucks.test': Table('test', MetaData(bind=Engine(postgresql://localhost/test)), Column('a', INTEGER(), table=<test>), schema='wow.this.sucks')})

[cpcloud]

Somewhat related: Should we discover all schemata in the database if just a database is given to resource?

For example:

d = Data('postgresql://localhost/db')
d.my_schema.table1  # not the default schema
d.table1  # public schema

We can merge this PR before deciding on this.

[llllllllll]

I think that would be a great addition; I will work on that as a separate pr. Does this pr look good though?

[cpcloud]

yep 👍