MT#58014 encrypt: Avoid remove leading / messages from tar

We are prepending an extra / to the pathnames passed to tar, and
calling tar from a directory other than the root directory while
not telling it to use absolute names so it complains about these
two things with the following messages:

  ,---
  tar: Removing leading `/' from member names
  tar: Removing leading `/' from hard link targets
  tar: Removing leading `//' from member names
  tar: Removing leading `//' from hard link targets
  `---

which is something the user cannot do much about, and it's rather
annoying.

Change-Id: I9e9c853f26363e451b8883d3c74c5508ba3049dc

scripts/decrypt

@@ -102,8 +102,10 @@ if ! gpg -d "${TARGZ}".gpg > "${TARGZ}" ; then
   log_error "Error while decrypting ${TARGZ}.gpg"
   RC=1
 else
-  cd / # important to extract files at according place
-  if tar zxf "${TARGZ}" ; then
+  # For backwards compatibility we switch to the root directory, for old
+  # encrypted tarballs that stripped the leading /.
+  cd /
+  if tar zxPf "${TARGZ}" ; then
     log_info "Successfully restored configuration archive ${TARGZ}.gpg"
     log_info "Now you should be able to run 'ngcpcfg apply' again."
   else

scripts/encrypt

@@ -30,8 +30,8 @@ get_config_file_list() {
       # if the file does not exist (e.g. because "ngcpcfg apply"
       # hasn't been executed yet for whatever reason, then don't
       # report missing files, otherwise tar will complain
-      if [ -r "/${y}" ] ; then
-        echo "/${y}"
+      if [ -r "${y}" ] ; then
+        echo "${y}"
       fi
     done
   done
@@ -61,7 +61,7 @@ fi
 
 TARGZ=/etc/ngcp-config-crypted.tgz
 
-tar zcf "${TARGZ}" /etc/ngcp-config/ "${FILES[@]}" /etc/.git
+tar zcPf "${TARGZ}" /etc/ngcp-config/ "${FILES[@]}" /etc/.git
 if gpg --symmetric "${TARGZ}" ; then
   log_info "Successfully created encrypted ngcpcfg configuration archive ${TARGZ}.gpg"
   # ensure we don't leave the unencrypted version behind