--features doesn't work for cargo metadata in projects with workspaces

[koute]

Steps to reproduce:

cargo new --lib foo
cd foo
echo '[workspace]' >> Cargo.toml
echo 'members = ["bar"]' >> Cargo.toml
cargo new --lib bar
cargo metadata --features dummy

This generates the following error on cargo 1.27.0-nightly (0a1add2 2018-04-20):

error: cannot specify features for more than one package

This completely breaks --features usage in cargo-web on nightly (koute/cargo-web#95).

It works as expected on stable. This is possibly related to #5364.

[alexcrichton]

I believe this was reverted and fixed in #5430, so closing in favor of that