Fix and improve /etc/exports updates (#60)

* Fix and improve /etc/exports changes. Properly remove old bindings. Make them machine-name dependent

* Fix the bug that changing shared dir to parent one would not update boot2docker configuration.

i.e. if old share was "/Users/macuser" and new one is "/Users" then isNFSMounted would wrongfully report that NFS already mounted

* Convert tabs to spaces for code style to be inline with the rest of the file

Author: achekulaev

docker-machine-nfs.sh

@@ -328,16 +328,32 @@ configureNFS()
 
   echoWarn "\n !!! Sudo will be necessary for editing /etc/exports !!!"
 
+  #-- Update the /etc/exports file and restart nfsd
+
+  local exports_begin="# docker-machine-nfs-begin $prop_machine_name"
+  local exports_end="# docker-machine-nfs-end $prop_machine_name"
+
+  # Remove old docker-machine-nfs exports
+  local exports=$(cat /etc/exports | \
+    tr "\n" "\r" | \
+    sed "s/${exports_begin}.*${exports_end}//" | \
+    tr "\r" "\n"
+  )
+
+  # Write new exports blocks beginning
+  exports="${exports}\n${exports_begin}\n"
+
   for shared_folder in "${prop_shared_folders[@]}"
   do
-    # Update the /etc/exports file and restart nfsd
-    (
-      echo '\n'$shared_folder' '$prop_machine_ip' '$prop_nfs_config'\n' |
-        sudo tee -a /etc/exports && awk '!a[$0]++' /etc/exports |
-        sudo tee /etc/exports
-    ) > /dev/null
+    # Add new exports
+    exports="${exports}$shared_folder $prop_machine_ip $prop_nfs_config\n"
   done
 
+  # Write new exports block ending
+  exports="${exports}${exports_end}"
+  #Export to file
+  echo "$exports" | sudo tee /etc/exports >/dev/null
+
   sudo nfsd restart ; sleep 2 && sudo nfsd checkexports
 
   echoSuccess "\t\t\t\t\t\tOK"
@@ -405,8 +421,8 @@ isNFSMounted()
 {
   for shared_folder in "${prop_shared_folders[@]}"
   do
-    local nfs_mount=$(docker-machine ssh $prop_machine_name "sudo df" |
-      grep "$prop_nfshost_ip:$prop_shared_folders")
+    local nfs_mount=$(docker-machine ssh $prop_machine_name "sudo mount" |
+      grep "$prop_nfshost_ip:$prop_shared_folders on")
     if [ "" = "$nfs_mount" ]; then
       echo "false";
       return;