Fix rm-data hanging when some OSDs are inactive, add a test for it

There's also another case which also needs to be fixed - we shouldn't retry
deletions for indefinite time if an OSD is stopped during deletion

tests/test_rm_degraded.sh

@@ -0,0 +1,25 @@
+#!/bin/bash -ex
+
+SCHEME=xor
+PG_COUNT=16
+PG_MINSIZE=2
+. `dirname $0`/run_3osds.sh
+
+build/src/cmd/vitastor-cli --etcd_address $ETCD_URL create -s 128M testimg
+
+LD_PRELOAD="build/src/client/libfio_vitastor.so" \
+    fio -thread -name=test -ioengine=build/src/client/libfio_vitastor.so -bs=4M -direct=1 -iodepth=1 \
+        -end_fsync=1 -fsync=1 -rw=write -etcd=$ETCD_URL -image=testimg -size=128M -cluster_log_level=10
+
+kill -9 $OSD3_PID
+$ETCDCTL del /vitastor/osd/state/3
+
+if build/src/cmd/vitastor-cli --etcd_address $ETCD_URL rm testimg --log_level 10 ; then
+    format_error "Delete should not be successful with inactive OSDs"
+fi
+
+if ! ( build/src/cmd/vitastor-cli --etcd_address $ETCD_URL ls | grep testimg | grep DEL ) ; then
+    format_error "Image should be marked as partially deleted"
+fi
+
+format_green OK