67 name file is not defined is shown in some checks

[monrog2]

switchover to open() and supress pexpect futurewarning in py3.8 env (ACI 6.0(2))

[monrog2]

6.0(2) tests passed
pytest on py2 ACI versions passed

admin@apic1:techsupport> python aci-preupgrade-validation-script.py
    ==== 2023-08-14T17-52-35+0000, Script Version v1.6.1  ====

!!!! Check https://github.com/datacenter/ACI-Pre-Upgrade-Validation-Script for Latest Release !!!!

To use a non-default Login Domain, enter apic#DOMAIN\\USERNAME
Enter username for APIC login          : admin
Enter password for corresponding User  : 

Checking current APIC version (switch nodes are assumed to be on the same version)...6.0(2h)

Gathering APIC Versions from Firmware Repository...

[1]: aci-apic-dk9.5.2.3g.bin
[2]: aci-apic-dk9.6.0.2h.bin

What is the Target Version?     : 1

You have chosen version "aci-apic-dk9.5.2.3g.bin"

Collecting VPC Node IDs...

[Check  1/47] APIC Target version image and MD5 hash... 
              Checking apic1......                                                                                                    DONE