fix: improve error handling in mikrotik/resourceRead() functions

[maksym-nazarenko]

fixes #63, fixes #65

Now instead of panic the output will look like:

mikrotik_pool.pool: Refreshing state... [id=*1]
mikrotik_script.bar: Refreshing state... [id=my_script]
╷
│ Error: from RouterOS device: invalid user name or password (6)
│ 
│   with mikrotik_pool.pool,
│   on main.tf line 16, in resource "mikrotik_pool" "pool":
│   16: resource "mikrotik_pool" "pool" {
│ 
╵
╷
│ Error: from RouterOS device: invalid user name or password (6)
│ 
│   with mikrotik_script.bar,
│   on main.tf line 22, in resource "mikrotik_script" "bar":
│   22: resource "mikrotik_script" "bar" {

[ddelnano]

Wow there were many inconsistencies 😬. Thanks for fixing this and I look forward to preventing new occurrences of these issues once #47 is complete.