XD 143

Provide redis config support for xd scripts
- Added a new config file under conf/redis.properties with default host/port
  this property file will be made available under XD_HOME/conf in spring-xd bundle
- Enabled redisHost & port options
- Added property placeholder configurer for the XD_HOME/conf/redis.properties
  and, make this "override" system properties mode
- Make xd scripts' commandLine options override existing redis conf
- Make redis properties always refer to XD_HOME/conf

Under spring-xd bundle,
xd/conf will have redis.properties
xd/bin/xd-container* xd/bin/xd-admin* scripts will have the commandLine options
"--redisHost" and "--redisPort" available to override existing xd/conf/redis.properties

Under development environment,
xd.home will always point to the relative path ".." and will refer the redis.properties
as "../conf/redis.properties"