apply: make sure each stage starts off back from the repo root dir

the apply.sh script should assume current directory is arbitrary after
executing each step: base, bitcoin, lnd and so on.

this commit simply changes current dir to the repo root before executing
every step.

apply.sh

@@ -3,15 +3,20 @@
 # it must be run as root or a user with equivalent privileges.
 
 exit_code=0
+# defined in the caller script
+rootdir="$SYSUPDATES_ROOTDIR"
 
 # base os
+cd "$rootdir"
 ./base/voidlinux.sh || exit 1
 
 # bitcoin core
+cd "$rootdir"
 . ./btc/env
 bitcoin_apply || exit_code=$?
 
 # lnd lightning
+cd "$rootdir"
 . ./lnd/env
 lnd_apply || exit_code=$?
 

update.sh

@@ -46,6 +46,7 @@ if [ $? -ne 0 ]; then
 fi
 
 # run repo's update script
+export SYSUPDATES_ROOTDIR="$REPODIR"
 export SYSUPDATES_CHANNEL="$BRANCH"
 ./apply.sh >> $LOGFILE 2>&1
 if [ $? -ne 0 ]; then