rust-bin.bbclass: look for RUNPATH instead of RPATH

Poky 1.7 uses RPATH is now RUNPATH, so update our grep string appropriately.

Additionally, bitbake is having trouble with the automatic RDEPENDS on
rustlib.  Make it explicit for now.

classes/rust-bin.bbclass

@@ -2,6 +2,7 @@ inherit rust
 
 RUSTLIB_DEP ?= " rustlib"
 DEPENDS .= "${RUSTLIB_DEP}"
+RDEPENDS_${PN} .= "${RUSTLIB_DEP}"
 DEPENDS += "patchelf-native"
 
 export rustlibdir = "${libdir}/rust"
@@ -101,7 +102,7 @@ do_rust_bin_fixups() {
 
     for f in `find ${PKGD}`; do
         file "$f" | grep -q ELF || continue
-        readelf -d "$f" | grep RPATH | grep -q rustlib || continue
+        readelf -d "$f" | grep RUNPATH | grep -q rustlib || continue
         echo "Set rpath:" "$f"
         patchelf --set-rpath '$ORIGIN:'${rustlibdir}:${rustlib} "$f"
     done