Allow ${variables} in Default parameters

[evshvarov]

It'd be great to be able to init parameters with ${variables}, like ${libdir} or ${ipmdir}. It can be very helpful while installing packages on different IRIS servers, and let packages behave according to these parameters.
I tried the following, and it didn't work :

<Default Name="datapath" Value="${libdir}data/" />

it ended up with the following error:

<REGULAR EXPRESSION>ReplaceAll+3^%Regex.Matcher.1