VarSet: Nami should not chomp on all 'Variable:' keys
VarSet: Nami should not chomp on all 'Variable:' keys

Previously Nami chomped all lines containing 'variable' in the key and tried
to fill `variables` hash with `KEY=VALUE` pairs from that.
Unfortunately Asterisk has this one command, where

```
Variable: KEY
Value: VALUE
```

https://wiki.asterisk.org/wiki/display/AST/Asterisk+11+ManagerEvent_VarSet

To avoid this I added additional check to distinguish VarSet syntax from other
commands and events.

tqcenglish/Nami,carragom/Nami,marcelog/Nami