Add attach/detach notifications

Add the following notifications:
  - attach.start
  - attach.end
  - detach.start
  - detach.end

Blueprint: attachment-notifications
Change-Id: I4a4b123468c139bc2bcd948a1e7438c3830b5e42
Don't stop volume service for failed re-export operations

Commit b71570 "Set vol driver initialized before deleting volumes"
changed the manager behavior to call set_initialized() before
attempting to re-export volumes.

Drivers should not be considered initialized before re-export has
succeeded.  Otherwise a failure to export causes the volume
service to stop, when that failure should be handled like any other
failure to initialize.

Closes-Bug: 1257049
Related-Bug: 1232177
Change-Id: Ic6bc89ef3f15dbbc971fdd8c91117cccb5c2801b
Add unit tests for volume reserve and unreserve

This adds unit tests for successful reserving and unreserving, and vice
versa for not being in the right status.

Change-Id: Iaa777055315251efa4a14976e25b9baab222f934
Bump to sqlalchemy-migrate 0.8.2

This allows us to drop some unsightly sqlalchemy-migrate 0.7.3
patching.

The related requirements change is here:

  Icde6248ca102884323d7912bab0f4a716aa294ec

Change-Id: I5f80dfc07f8256716d025002fc1a1f47e58b2142
Adjust RBD delete log level

Set notice of volume no longer existing in RBD backend when attempting
to delete to log INFO level. Also move a comment next to related code.
This is a follow-up to suggestions from
3de7da12d1098ef777305099e5f4a039e536bf99.

Change-Id: I3ff854e0ead79e208106a371e14ec6ac7603d387
Change method name to test_get_volume_stats

Change test method name from test_update_volume_stats2 to
test_get_volume_stats in cinder/tests/test_eqlx.py.

It was pointed out by Change-Id:
I0642bdb911ca72517ed655f795e0055f4c4654b8

Change-Id: Id21c67e3e1151573e69ef21714fbf493f62ad425
Use model_query() in db.*****_destroy

Use model_query() instead of session.query in db.volume_destroy,
db.volume_type_destroy, db.transfer_destroy and db.snapshot_destroy as
other methods use.
model_query function is the query helper which is used in most part of
cinder/db/sqlalchemy/api.py.

Change-Id: I97be252df9d40bb97231e3341d5cedec26af2d93
Closes-Bug: #1256483
Add more logging to migrate_volume_completion

Add a debug message on entering the function, and an info message if
it was called to clean up an error. This is useful because Nova copies
the data of in-use volumes, and if it fails there will only be a
message in the Nova logs.

Change-Id: I546d0bae8639072727ebe23394885d40255ba1d4
Fix typo/misspelled words

Fix type/misspelled words found by this handy tools:
https://github.com/lyda/misspell-check

Some 'typo's were intentional since they are part of function name,
so they are left alone.

Change-Id: I4badda869521659b541d018727a6f71f518e2ee0
Merge "Adjust RBD delete log level"
Merge "Use model_query() in db.*****_destroy"
Merge "Add more logging to migrate_volume_completion"
Merge "Don't stop volume service for failed re-export operations"
Merge "Bump to sqlalchemy-migrate 0.8.2"
Merge "Add unit tests for volume reserve and unreserve"
Merge "Add attach/detach notifications"
Merge "Change method name to test_get_volume_stats"