sysutils/vmdktool: Set TEST_TARGET and WWW, and fix ALL_TARGET

• Set TEST_TARGET. We need a utility called prove that comes with Perl 5 so set USES=perl5 as well.
• Set ALL_TARGET to vmdktool. The default one, all, attempts to build vmdktool.8.gz using Groff. Since the final vmdktool.8.gz is never not installed anyway (the install target always installs the original vmdktool.8), it is better to just change the ALL_TARGET to vmdktool directly. This way we do not add dependencies to the build phase.
• Set WWW to give users at least some information, even though the project does not have its official homepage.

Reviewed by: garga
Approved by: maintainer (garga)
Differential Revision: https://reviews.freebsd.org/D21464