Fix failing darwin tests

Some tests were failing on darwin,
if the auto-allocate-uids featrure was enabled.
This was because AAU on darwin works by setuid-ing as a non-existent
user, so the tests that were relying on `whoami` were failing.

In the case of trusted-users we fall back to printing the user id,
which is already handled gracefully in the daemon code - i.e. when
a user does not exist or for some other reason looking up their
username is not possible, the daemon falls back to searching for their
uid inside the trusted-users list.

When whoami is used to print the username for other purpose,
we default to printing nixbld.

Change-Id: Id65a091948c94f0eda8af964f1a23c403a27afc5

tests/functional/bash-profile.sh

@@ -2,7 +2,7 @@ source common.sh
 
 sed -e "s|@localstatedir@|$TEST_ROOT/profile-var|g" -e "s|@coreutils@|$coreutils|g" < ../../scripts/nix-profile.sh.in > $TEST_ROOT/nix-profile.sh
 
-user=$(whoami)
+user=$(whoami || echo -n nixbld)
 rm -rf $TEST_HOME $TEST_ROOT/profile-var
 mkdir -p $TEST_HOME
 USER=$user $SHELL -e -c ". $TEST_ROOT/nix-profile.sh; set"

tests/functional/init.sh

@@ -28,7 +28,7 @@ substituters =
 flake-registry = $TEST_ROOT/registry.json
 show-trace = true
 include nix.conf.extra
-trusted-users = $(whoami)
+trusted-users = $(whoami || id -u)
 EOF
 
 cat > "$NIX_CONF_DIR"/nix.conf.extra <<EOF