switchroot: Fix test-switchroot now autotools can build static

This test previously depended on manually building ostree-prepare-root.
Since 42dab85 we've been able to build static binaries with the usual
autotools build-system.  This change reflects the fact that
`ostree-prepare-root` is built into $srcdir rather than `src/switchroot`
where I was building manually.

This test now passes with `./configure --with-static-compiler=gcc` (glibc)
but still fails with `./configure --with-static-compiler=musl-gcc` (musl).

Closes: #485
Approved by: cgwalters

tests/test-switchroot.sh

@@ -6,7 +6,7 @@ setup_bootfs() {
 	mkdir -p "$1/proc" "$1/bin"
 	echo "quiet ostree=/ostree/boot.0 ro" >"$1/proc/cmdline"
 	touch "$1/this_is_bootfs"
-	cp "$(dirname "$this_script")/../src/switchroot/ostree-prepare-root" "$1/bin"
+	cp "$(dirname "$this_script")/../ostree-prepare-root" "$1/bin"
 }
 
 setup_rootfs() {