Raise key length defaults

Extend RSA keylength to 2048 bits by default,
as the previous default of 1024 bit is considered
weak since 12/31/2010.

Also unify the message_md to the openssl builtin default.

Fixes bug 1103002

Change-Id: I70e90b7696f8a56073c3d6bdc9ed5d30cfa3401f
Check schema when dropping constraints.

MySQL constraints are not named like others.

Previous to this patch, we were looking up the names in MySQL's
INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS table, but were
neglecting to also check the Schema. The same table
could be in multiple schemas; as an example a unit test
run on the same machine as devstack in two different schemas
but the same RDBMS.

This patch uses a better approach. Sqlalchemy knows about the
name of the constraint, it just doesn't use it in the
drop statement by default. The Constraint objects from
the main sqlalchemy package don't do drops, only those out
of the migrate package. This patch finds the name of the
constraint in the constraint bound to the table and passes it
to the migrate ForeignKeyConstraint to use in the drop statement

Bug 1186353

Change-Id: Ida2184021de9dd220a36507a8a625cf4210d17f7
Missing contraction: Its -> It's (bug 1176213)

Change-Id: I9403289012eea3b78f9bf02154827554d9e07462
Merge "Check schema when dropping constraints."
Merge "Missing contraction: Its -> It's (bug 1176213)"
Merge "Raise key length defaults"