Add db table for Glance Metadata

This commit implements the blueprint
https://blueprints.launchpad.net/cinder/+spec/retain-glance-metadata-for-billing

It creates the new table volume_glance_metadata in the cinder
database, provides the CRUD methods for it, and populates the table
when a volume or snapshot is created from a Glance image.

Patch set 2: remove superflous line

Patch set 3: Fix incorrect column types in sqlalchemy/models.py

Patch set 4: Define exception class GlanceMetadataExists

Change-Id: I8f98f6eaae005a33bfd49cea783774407b7aa120

cinder/db/sqlalchemy/models.py

@@ -21,7 +21,7 @@
 SQLAlchemy models for cinder data.
 """
 
-from sqlalchemy import Column, Integer, String, schema
+from sqlalchemy import Column, Integer, String, Text, schema
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import ForeignKey, DateTime, Boolean
@@ -205,6 +205,16 @@ class VolumeTypeExtraSpecs(BASE, CinderBase):
     )
 
 
+class VolumeGlanceMetadata(BASE, CinderBase):
+    """Glance metadata for a bootable volume"""
+    __tablename__ = 'volume_glance_metadata'
+    id = Column(Integer, primary_key=True, nullable=False)
+    volume_id = Column(String(36), ForeignKey('volumes.id'))
+    snapshot_id = Column(String(36), ForeignKey('snapshots.id'))
+    key = Column(String(255))
+    value = Column(Text)
+
+
 class Quota(BASE, CinderBase):
     """Represents a single quota override for a project.
 
@@ -378,6 +388,7 @@ def register_models():
               VolumeMetadata,
               VolumeTypeExtraSpecs,
               VolumeTypes,
+              VolumeGlanceMetadata,
               )
     engine = create_engine(FLAGS.sql_connection, echo=False)
     for model in models: