Move vpn_key_suffix into pipelib

Apart from one use in the EC2 API, vpn_key_suffix is only used in
pipelib.

blueprint: scope-config-opts
Change-Id: If90b9e77905161ea8d9263e8bae2c47ac5f79e91
Move service_down_time to nova.service

blueprint: scope-config-opts
Change-Id: I5fddb3768348c43a38b72dbf738b0c7fa2967691
Move memcached_servers opt into common.memorycache

Add a factory function to nova.common.memorycache which consolidates
the code to choose between real or fake memcache. This then means that
memcached_servers is used in just one place and we can move the config
option there.

blueprint: scope-config-opts
Change-Id: I67c191e0db58364eda4162b9e881606063509b9d
Move global service networking opts to new module

The my_ip, host and use_ipv6 options are used all over the codebase
and they're pretty well related to each other. Create a new netconf
module for them to live in.

There are now no options registered globally in nova.config!

blueprint: scope-config-opts
Change-Id: Ifde37839ae6f38e6bf99dff1e80b8e25fd68ed25
Remove unused opt import in scheduler.driver

Reported by Joe Gordon.

Change-Id: I8d48cad8f7f1548d20f0c3c0d8a4b11dcc351cf4
Remove unused baremetal PXE options

These options were introduced by commit a2f260f and appear to never to
have been used.

Change-Id: Idf1387fd453b7b1c392db764934c148dcbfc5d66
Merge "Move vpn_key_suffix into pipelib"
Merge "Move service_down_time to nova.service"
Merge "Move memcached_servers opt into common.memorycache"
Merge "Move global service networking opts to new module"
Merge "Remove unused opt import in scheduler.driver"
Merge "Remove unused baremetal PXE options"