Support version growing.

When new version released, edit version.py to set new version number.

Change-Id: I949734c95969c4a93ecbf1ffbeebc77c335bf262
Sort out config file

Make all config information into one file named 'postman.conf'

Change-Id: I4c7c2777f9864e15a8e3cb66296308bd924d89f9
Add floating-ip model support, and enhance database manage.

Change-Id: I2e12adedc050ea40ef4bcbf60e2ea6b91f15271a
Enhance postman-manager

Change-Id: Ibb11c76fadce918403847c5f97e237219940ed63
Print sql_connection when do db_sync and db_version

Change-Id: I93c9f4d38d37213e7c5607db7483986bde3a5187
Add support for use floating-ip.

Create new config entry named 'use_floating_ip_pool'. If the config entry is
set, new loadbalancer, vip will have floating-ip, and vip to end user will set
to floating-ip. Besides, it will use floating-ip to loggin loadbalancer to do
configurations.

BTW, Check user request when create node. If the request instance's metadata
not valid, just raise 400.

Change-Id: Id945cef57af5296fdeddcd3d6bc2a297d4dd1e95
Update readme for attantion

Change-Id: If651fae7c643399d80d8d79ad87c6cf1fb35c1c2