Support "configure session"

[codeout]

Issue: eAPI doesn't support atomic operations

When we run commands below via eAPI, we'll see an error saying "Address 172.16.0.1 is already assigned to interface Ethernet6" at L7, and L1-L6 are committed.

However, sometimes I'd like to do this as an atomic operation, where abort everything when something goes wrong.

This PR will support that behavior with introducing Node#configure_session().

1: interface Ethernet6
2:    no switchport
3:    ip address 172.16.0.1/30
4: !
5: interface Ethernet7
6:    no switchport
7:    ip address 172.16.0.1/30  ! Invalid

{
  "jsonrpc": "2.0",
  "method": "runCmds",
  "params": {
    "format": "json",
    "timestamps": false,
    "autoComplete": false,
    "expandAliases": false,
    "cmds": [
      "configure",
      "interface Ethernet6",
      "   no switchport",
      "   ip address 172.16.0.1/30",
      "interface Ethernet7",
      "   no switchport",
      "   ip address 172.16.0.1/30"
    ],
    "version": 1
  },
  "id": "EapiExplorer-1"
}

Usage

node = pyeapi.connect_to('veos01')
vlans = node.api('vlans')

node.configure_session()
vlans.create(100)  # Sends "configure session 9c27d0e8-afef-4afd-95ae-3e3200bb7a3e" and "vlan 100"

node.diff()  # Sends "configure session 9c27d0e8-afef-4afd-95ae-3e3200bb7a3e" and "show session-config diff" 
"""
=>
--- system:/running-config
+++ session:/9c27d0e8-afef-4afd-95ae-3e3200bb7a3e-session-config
@@ -32,7 +32,7 @@
 !
 clock timezone Asia/Tokyo
 !
-vlan 1000,3001-3006
+vlan 100,1000,3001-3006
 !
 interface Port-Channel1
    switchport trunk allowed vlan 3001-3003
"""

node.abort()  # Sends "configure session 9c27d0e8-afef-4afd-95ae-3e3200bb7a3e" and "abort" 
# or
node.commit() # Sends "configure session 9c27d0e8-afef-4afd-95ae-3e3200bb7a3e" and "commit" 
"""

When there is something invalid:

node = pyeapi.connect_to('veos01')
interfaces = node.api('interfaces')

if not (interfaces.configure(['interface Eth6', 'no switchport', 'ip address 172.16.0.1/30']) and \
    interfaces.configure(['interface Eth7', 'no switchport', 'ip address 172.16.0.1/30'])):
    node.abort()  # This aborts everything!!

Note

If Node#configure_session() isn't called, nothing changed in library behavior.

Test result

With vEOS below,

Software image version: 4.22.0F
Architecture:           i386
Internal build version: 4.22.0F-12170486.4220F
Internal build ID:      2c34e816-9aa7-4c63-9a32-05140aec7dbd

I haven't broken anything hopefully, and I don't see any performance impact here.

develop branch:

$ grep -A2 Ran result.develop
Ran 415 tests in 0.348s

OK
--
Ran 282 tests in 107.999s

FAILED (failures=7)

PR branch:

$ grep -A2 Ran result.pr
Ran 415 tests in 0.348s

OK
--
Ran 282 tests in 103.887s

FAILED (failures=7)