Stop overriding CONF.default_log_levels per binary

Overriding CONF.default_log_levels means we loose some explicitly set
default values such as 'iso8601=WARN'. Also explicitly overriding
CONF.default_log_levels means that default_log_levels cannot be set in a
config file.

Change-Id: Ib5103b88ec3f9ccd9d516032c6a13dc2fa4bcb5e
Fix early resource property value validation

Currently resource property validation fails if resource it
depends on is not created.

This change skips a property constraint validation if its intrinsic
function resolution does not find the dependant resource.

Change-Id: I2056c89437e8df2a59726b60c3c12f19f713d84d
Partial-Bug: #1317636
Pass user_creds_id when creating backup stack

When creating a backup stack on update, we don't want to create a
new user_creds record, or update won't work with a trust-scoped
token.  So instead pass the existing stack user_creds_id in to the
constructor when creating the backup stack.

The current behavior is actually doubly wrong, since we don't delete
user_creds records when deleting the backup stack, so the stale
creds records are probably left behind in the DB.

Change-Id: I6bd0568fdf5301b876c40acddc73542bcfc224e3
Partial-Bug: #1342593
Implement trove client plugin

This moves the client creation code out of Clients._trove() into
its own client plugin.

Trove is an integrated project, and python-troveclient is a dependency,
so the import is now mandatory.

Change-Id: I89d290f6a38488779e77ff11bdfdd64c159a57e8
Implement ceilometer client plugin

This moves the client creation code out of Clients._ceilometer() into
its own client plugin.

Ceilometer is an integrated project, and python-ceilometerclient
is a dependency, so the import is now mandatory.

Change-Id: Id4961c4d9678d7bfe3739128843c41921cc8a34b
Implement heat client plugin

This moves the client creation code out of Clients._heat() into
its own client plugin.

Clients._get_client_option is no longer used, so has been deleted

Change-Id: Ie14906b6cc605d6db49a5153ffa27f82debcc430
Merge "Fix early resource property value validation"
Merge "Pass user_creds_id when creating backup stack"
Merge "Stop overriding CONF.default_log_levels per binary"
Merge "Implement trove client plugin"
Merge "Implement ceilometer client plugin"
Merge "Implement heat client plugin"