testsuite: fix FLUX_HWLOC_XMLFILE test under flux-run(1)

Problem: When used under flux-run(1), the FLUX_HWLOC_XMLFILE test in
t0001-basic.t may fail due to CPU affinity.

Before launching flux-start(1), use hwloc-bind(1) to undo any CPU
affinity mask so that the expected resources from the fake hwloc XML
are available in output.

t/t0001-basic.t

@@ -370,10 +370,11 @@ test_expect_success 'flux-start dies gracefully when run from removed dir' '
 '
 
 command -v hwloc-ls >/dev/null && test_set_prereq HWLOC_LS
-test_expect_success HWLOC_LS 'FLUX_HWLOC_XMLFILE works' '
+command -v hwloc-bind >/dev/null && test_set_prereq HWLOC_BIND
+test_expect_success HWLOC_LS,HWLOC_BIND 'FLUX_HWLOC_XMLFILE works' '
 	hwloc-ls --of xml -i "numa:2 core:3 pu:1" >test.xml &&
-	FLUX_HWLOC_XMLFILE=test.xml flux start -s 2 flux resource info \
-		>rinfo.out &&
+	FLUX_HWLOC_XMLFILE=test.xml hwloc-bind all \
+		flux start -s 2 flux resource info >rinfo.out &&
 	test_debug "cat rinfo.out" &&
 	grep "12 Cores" rinfo.out
 '