New activemq_systemd_expand_environment parameter

[guidograzioli]

When the new parameter is set to true:

Variable	Description	Default
activemq_systemd_expand_environment	Whether or not to expand the environment in the sysconfig file. If true, environment file is sourced and the activemq process is started in a shell	false

the systemd unit template is changed to run the activemq process in a shell, sourcing the sysconfig environment file just before exection. This allows to use shell expansions in the environment file.

Examples:

activemq_systemd_expand_environment: true
activemq_java_opts_mem: '-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/var/log/amq_$(date "+%Y%m%d_%H%M%S").hprof'