Closes #329

Added support for expanding environment variables in configuration files.

For example:

Given an example node.properties files

node.environment=${ENV}
node.data-dir=/var/lib/presto/data
node.launcher-log-file=/var/log/presto/launcher.log
node.server-log-file=/var/log/presto/server.log
catalog.config-dir=/etc/presto/catalog
plugin.dir=/usr/lib/presto/lib/plugin

application can now resolve variable defined by ${ENV} from environment variables.

• Definitions of a variable are ${variableName} or $variableName. In addition to this, on Windows, %variableName% definition is supported as well.
• In case of an invalid or non existing variable definition, variable is left unchanged.