*: explicitly print "exit" at the end of every node config

*: explicitly print "exit" at the end of every node config

There is a possibility that the same line can be matched as a command in
some node and its parent node. In this case, when reading the config,
this line is always executed as a command of the child node.

For example, with the following config:
```
router ospf
 network 193.168.0.0/16 area 0
!
mpls ldp
 discovery hello interval 111
!
```
Line `mpls ldp` is processed as command `mpls ldp-sync` inside the
`router ospf` node. This leads to a complete loss of `mpls ldp` node
configuration.

To eliminate this issue and all possible similar issues, let's print an
explicit "exit" at the end of every node config.

This commit also changes indentation for a couple of existing exit
commands so that all existing commands are on the same level as their
corresponding node-entering commands.

Fixes #9206.

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>