Using async pysnp getCmd

[Tonygratta]

Bugfix #3469 The sync pysnmp API has been deprecated and removed since version 6.2.0. This commit replaces sync getCmd with async getCmd pysnmp method.

[ktbyers]

@Tonygratta I didn't realize this had been moved to an async solution. This won't work for Netmiko which is entirely synchronous.

[ktbyers]

Let me look at this some more...

[ktbyers]

I think we need to make this backwards compatible i.e. try to use the old solution first and then only try the new solution if the old doesn't work.

I say this as the new solution is very new and they changed the code meaningfully (i.e. they converted over to an async solution).

Let me know if you want to take a first pass on this, if not, I will do it.

[ktbyers]

Pattern should probably be to detect old solution/new solution here:

try:
    from pysnmp.entity.rfc3413.oneliner import cmdgen
    SNMP_MODE = "legacy"
except ImportError:
    from pysnmp.hlapi.asyncio import cmdgen
    SNMP_MODE = "async"
except ImportError:
    raise ImportError("pysnmp not installed; please install it: 'pip install pysnmp'")

Something like that and then use that SNMP_MODE flag to pick/use the right code.

We also need to anticipate people might need the older version of SNMP for quite some time (especially since the new SNMP is not-backwards compatible).

[ktbyers]

FYI, I started working on this.

[ktbyers]

Superseded by:

#3473