Replaced calls of get(foo, None) -> get(foo)

If no default value is specified, the get method of dictionaries
defaults to 'None' already.
So removing the 'None' argument to make the code more clean and
readable.

Change-Id: I2f29315488d515aa2837d06ea59ab41e8ca05fc8
Refactor UUID test

Oslo is removing uuidutils during the icehouse cycle. We had removed
uuidutils.generate_uuid() in https://review.openstack.org/#/c/60643/
It seems the UUID test was not executed, for example, there is no method
called generate_uuid() in common/utils, the Jekins still passed. This
patch move the testcase and remove the test method for generate_uuid.

Change-Id: If4f508129f0b44d63fe77ed1251c0e0737e7e897
Partial-Bug: #1253497
Sync common db code from Oslo

This sync contains commit ``ce69e7f Don't store engine instances in oslo.db ``
which removed global engine from oslo.db code. So, added code
for work with sqla engines and sessions to Glance - get_engine()
and get_session() functions in glance.db.sqlalchemy.api module.

Also this remove database slave connection and tpool features, because
they was removed from oslo code and seeps to be unused in Glance.

Full list of changes:

7959826 db: move all options into database group
dda24eb Introduce mysql_sql_mode option, remove old warning
0b5af67 Introduce a method to set any MySQL session SQL mode
8dccc7b Handle ibm_db_sa DBDuplicateEntry integrity errors
0f24d82 Fix migration.db_version when no tables
ac84a40 Update log translation domains
c0d357b Add model_query() to db.sqlalchemy.utils module
84254fc Fix a small typo in api.py
b8a676c Remove CONF.database.connection default value
86707cd Remove None for dict.get()
0545121 Fix duplicating of SQL queries in logs
fcf517d Update oslo log messages with translation domains
fa05b7c Restore the ability to load the DB backend lazily
630d395 Don't use cfg.CONF in oslo.db
ce69e7f Don't store engine instances in oslo.db
35dc1d7 py3kcompat: remove
b4f72b2 Don't raise MySQL 2013 'Lost connection' errors
271adfb Format sql in db.sqlalchemy.session docstring
0334cb3 Handle exception messages with six.text_type
eff69ce Drop dependency on log from oslo db code
7a11a04 Automatic retry db.api query if db connection lost
11f2add Clean up docstring in db.sqlalchemy.session
1b5147f Only enable MySQL TRADITIONAL mode if we're running against MySQL
39e1c5c Move db tests base.py to common code
986dafd Fix parsing of UC errors in sqlite 3.7.16+/3.8.2+
9a203e6 Use dialect rather than a particular DB API driver
1779029 Move helper DB functions to db.sqlalchemy.utils
bcf6d5e Small edits on help strings
ae01e9a Transition from migrate to alembic
70ebb19 Fix mocking of utcnow() for model datetime cols
7aa94df Add a db check for CHARSET=utf8
aff0171 Remove "vim: tabstop=4 shiftwidth=4 softtabstop=4" from headers
fa0f36f Fix database connection string is secret
8575d87 Removed copyright from empty files
d08d27f Fix the obsolete exception message
8b2b0b7 Use hacking import_exceptions for gettextutils._
9bc593e Add docstring for exception handlers of session
855644a Removal of _REPOSITORY global variable.
ea6caf9 Remove string.lowercase usage
a33989e Remove eventlet tpool from common db.api
e40903b Database hook enabling traditional mode at MySQL
f2115a0 Replace xrange in for loop with range
c802fa6 SQLAlchemy error patterns improved
1c1f199 Remove unused import
97d8cf4 Remove lazy loading of database backend

Co-authored-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>

Related to blueprint db-use-oslo-common-code

Change-Id: Ia73abba8309ccc2ad10a0f636b410984c6b6e5d8
Merge "Refactor UUID test"
Documentation for Glance tasks

Added some docs for:-
    - configuration
    - notifications
    - statuses

partially implements blueprint async-glance-workers

Change-Id: I4e33bc3be2278d6906968d1dac3aff6587eef6df
Merge "Documentation for Glance tasks"
Merge "Sync common db code from Oslo"
Merge "Replaced calls of get(foo, None) -> get(foo)"