Append maven bin path to beginning of PATH

Append the MAVEN_HOME/bin path to the beginning of PATH environment
variable instead of at the end, so that the user picks up the
Puppet-installed Maven instance by default.

This is essentially the same fix that was applied to the puppet-java module 5 months ago:

https://github.com/7terminals/puppet-java/commit/27040f21dde638f5f0b6ddf398054b8682eb72c2