devel/cargo: Update to 0.17.0

[dumbbell]

Summary

Beside the version update, the port received the following changes:

• All ${DISTFILES} are now written to ${DISTDIR}/rust.
• Both distinfo were combined in a single file.
• The Cargo boostrap was updated to the same as lang/rust*.

Test Plan

Poudriere testport on HEAD/amd64 and 11.0/i386

[jbeich]

Can you skip 0.16.0 to 0.17.0? cargo-0.17.0 doesn't requrie pkg-plist changes and builds fine with rust-1.15.1 on [ 10.3 i386 | 10.3 amd64 | 11.0 i386 | 11.0 amd64 | 12.0 amd64 ].

Reminder: www/firefox >= 54.0 (on 2017-06-13) would require devel/cargo >= 0.16.0. Our buildbot has been busted for a few weeks.

[dumbbell]

Update to 0.17.0

[jbeich]

If the update slips 2017Q2 (early April) branch date please mark the commit for MFH as Firefox 54 is scheduled before 2017Q3 (early July).