build: Run all the tests against the just-built daemon.

* test-env.in: New file.
* configure.ac: Add it to `AC_CONFIG_FILES' and `commands-exec'.
* config-daemon.ac: Set and substitute `GUIX_TEST_ROOT'.
* Makefile.am (SCM_LOG_COMPILER, SH_LOG_COMPILER): Use it in lieu of
  `pre-inst-env'.
* daemon.am (test_root): Remove
  (AM_TESTS_ENVIRONMENT): Remove `TEST_ROOT'.
  (clean-local): Use $(GUIX_TEST_ROOT); make files writable before
  removing them.guix_test_root
* tests/guix-daemon.sh: Remove `NIX_' variable settings; don't launch
  `guix-daemon'.

tests/guix-daemon.sh

@@ -22,27 +22,8 @@
 
 set -e
 
-NIX_SUBSTITUTERS=""		# don't resort to substituters
-NIX_IGNORE_SYMLINK_STORE=1	# in case the store is a symlink
-NIX_STORE_DIR="$TEST_ROOT/store"
-NIX_LOCALSTATE_DIR="$TEST_ROOT/var"
-NIX_LOG_DIR="$TEST_ROOT/var/log/nix"
-NIX_STATE_DIR="$TEST_ROOT/var/nix"
-NIX_DB_DIR="$TEST_ROOT/db"
-NIX_ROOT_FINDER="$top_builddir/nix/scripts/list-runtime-roots"
-export NIX_SUBSTITUTERS NIX_IGNORE_SYMLINK_STORE NIX_STORE_DIR	\
-    NIX_LOCALSTATE_DIR NIX_LOG_DIR NIX_STATE_DIR NIX_DB_DIR	\
-    NIX_ROOT_FINDER
-
 guix-daemon --version
 guix-build --version
 
-# Launch the daemon without chroot support because is may be
-# unavailable, for instance if we're not running as root.
-guix-daemon --disable-chroot &
-
-daemon_pid=$!
-trap "kill $daemon_pid" EXIT
-
 guix-build -e '(@ (distro packages bootstrap) %bootstrap-guile)'
 guix-build coreutils -n