Remove xenapi rpm building code

Nova shouldn't be building any types of packages. And if we are we should
be testing this code in gate somewhere.

Change-Id: I70d82a6173b5eda183d4e49d330ae97dd14f9078
Remove duplicates from exceptions list

Duplicated exceptions:
 exception.QuotaError
 exception.SecurityGroupLimitExceeded

Change-Id: Ie8d40cf6e0a1a7b2191877059b757a752aeb4e29
Nova db/api.py docstring cleanups...

We no longer use LazyPluggable for the db_backend, and
dbapi_use_tpool options. These now come from
nova.openstack.common.db.api.

Also, removed doc about enable_new_services which seemed a bit
lonely without the rest and probably isn't needed since the
config option help explains it well enough.

Change-Id: I14d00e013a1a0c0dfc80e0bba8ad82e97940d6ac
Merge "Nova db/api.py docstring cleanups..."
Merge "Remove xenapi rpm building code"
Merge "Remove duplicates from exceptions list"