Added alembic migrations

Added alembic dependency to requirements
Created alembic config files

To create alembic migration:
$ cd ./ceilometer/storage/sqlalchemy/alembic
$ alembic revision -m "migration_description"

Related to blueprint convert-to-alembic

Change-Id: I59cf409106e0ba8bb819f7fc6aeddd0a837fee4c

ceilometer/storage/sqlalchemy/alembic/README

@@ -0,0 +1 @@
+Generic single-database configuration.

ceilometer/storage/sqlalchemy/alembic/alembic.ini

@@ -0,0 +1,51 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+script_location = %(here)s
+
+# template used to generate migration files
+# file_template = %%(rev)s_%%(slug)s
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# This is set inside of migration script
+# sqlalchemy.url = driver://user:pass@localhost/dbname
+
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARN
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = WARN
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

ceilometer/storage/sqlalchemy/alembic/env.py

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+from __future__ import with_statement
+from alembic import context
+from logging.config import fileConfig
+
+import ceilometer.openstack.common.db.sqlalchemy.session as sqlalchemy_session
+from ceilometer.storage.sqlalchemy import models
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+target_metadata = models.Base.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline():
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    url = config.get_main_option("sqlalchemy.url")
+    context.configure(url=url)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online():
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    engine = sqlalchemy_session.get_session().get_bind()
+
+    connection = engine.connect()
+    context.configure(connection=connection, target_metadata=target_metadata)
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

ceilometer/storage/sqlalchemy/alembic/script.py.mako

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+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision}
+Create Date: ${create_date}
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = ${repr(up_revision)}
+down_revision = ${repr(down_revision)}
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+def upgrade():
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade():
+    ${downgrades if downgrades else "pass"}

ceilometer/storage/sqlalchemy/alembic/versions/README

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+Directory for alembic migration files

requirements.txt

@@ -6,6 +6,7 @@ iso8601
 argparse
 SQLAlchemy>=0.7,<=0.7.99
 sqlalchemy-migrate>=0.7.2
+alembic>=0.4.1
 pymongo>=2.2
 eventlet
 anyjson>=0.3.3