support CLEAR_BKFILE envvar to remove bkfile

zfsbk.sh

@@ -18,6 +18,7 @@ usage () {
     echo
     echo "Optional envvars:"
     echo "UPLOAD_PATH   upload generated backup to this path. scp:// or rsync://"
+    echo "CLEAR_BKFILE  remove local backup file at the end of the process."
 }
 
 failmsg () {
@@ -115,3 +116,10 @@ then
     fi
 fi
 
+# remove backup file if requested
+if [ "x$CLEAR_BKFILE" = x ]
+then
+    rm -f $bkfile
+fi
+
+if