Add support for testing features that require a nightly Rust build

Certain features require a nightly build of the Rust toolchain. For
example, the peer credentials authenticator currently (Sep 2020)
requires the nightly Rust compiler, because the `peer_cred`
functionality it depends on is only available in the nightly builds.
Nonetheless, we still want to be able to test this functionality. This
commit adds a section to the CI script to allow us to test these sorts
of features with the nightly Rust toolchain.

Signed-off-by: Joe Ellis <joe.ellis@arm.com>

ci.sh

@@ -122,6 +122,15 @@ fi
 echo "Unit, doc and integration tests"
 RUST_BACKTRACE=1 cargo test $FEATURES
 
+# Run tests for Parsec features that require a nightly version of the compiler
+# to function. For example: Unix peer credentials authenticator is currently
+# only functional if we use the nightly compiler, since it depends on the
+# `peer_cred` function.
+# TODO: change this list as features trickle into the stable branch.
+echo "Nightly features"
+NIGHTLY_FEATURES="--features=peer-credentials-authenticator"
+RUST_BACKTRACE=1 cargo test +nightly $NIGHTLY_FEATURES
+
 # Removing any mappings left over from integration tests
 rm -rf mappings/