Use tar-ustar format for the dist archive

Use tar-ustar format for the dist archive

By default, Automake uses the old tar v7 format, which does not
support file paths longer than 99 characters. With the upcoming
Java agent refactoring, this becomes a problem.

This patch switches to the newer tar-ustar format, which supports
longer file paths in the archive.

Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>