VMWare Driver - Ignore datastore in maintenance mode

A datastore can be part of a datastore cluster. Any
datastore which is part of a cluster can be put in maintenance
mode. Instances cannot reside on a datastore if it is in
maintenance mode.
This fix ignores a datastore in the following scenarios
1. Stats update - Ignore a datastore during stats update.
2. Ignore a datastore during instance spawn.

Change-Id: Id0cb3f5fdb4d0bc4884cf5405fadc433d4a2b6ba
Closes-Bug: #1330065
Libvirt: Do not raise ENOENT exception

If the disk disappears during update_status(), only need to print
a warning, and do not need to raise an exception.

Change-Id: I87800c855c7b349f69163e33031404ad25e2a9ca
Closes-Bug: 1358609
Allow three periodic tasks to hit slave

Allows the following periodic tasks to hit a slave
if a slave_connection is configured:

_run_pending_deletes
_instance_usage_audit
_poll_volume_usage

Blueprint: juno-slaveification
Change-Id: I38585562e3d3579299e32b5f9ced9311f672abcc
Send create.end notification even if instance is deleted

There was an unprotected instance.save() call which could raise an
exception and bypass a create.end notification.  This adds a try/except
block around that call with appropriate handling of the exception.

Change-Id: I308ee84f6ab2bb37ef6570ff896017615a5bf746
Closes-bug: #1358795
Handle non-ascii characters in spawn exception msg

If a compute driver's spawn function returns an exception whose text
has any non-ascii characters (e.g., for globalization), the compute
manager's "reschedule logic" doesn't handle it properly as it runs
the text through the str() function, which causes UnicodeEncodeError
exceptions.

This simply sends the exception text through six.text_type so as to
no longer blow up and proceed with rescheduling as intended.

Closes-Bug: #1359427

Change-Id: I3fef783feffbe99c6971543c881e3fce2b60693b
Merge "VMWare Driver - Ignore datastore in maintenance mode"
Merge "Allow three periodic tasks to hit slave"
Merge "Libvirt: Do not raise ENOENT exception"
Merge "Send create.end notification even if instance is deleted"
Merge "Handle non-ascii characters in spawn exception msg"