Allow running all the tests with the daemon

When `NIX_DAEMON_PACKAGE` is set, make all the tests use the Nix daemon.
That way we can test every piece of Nix functionality both with and
without the daemon.

Tests for which using the daemon isn’t possible or doesn’t make sens can
selectively be disabled with `needLocalStore`

tests/binary-cache.sh

@@ -1,5 +1,7 @@
 source common.sh
 
+needLocalStore "“--no-require-sigs” can’t be used with the daemon"
+
 # We can produce drvs directly into the binary cache
 clearStore
 clearCacheCache