Tektronix5014C keeps data in buffer

If you encounter a bug use the following template.
If you have a feature request feel free to freestyle.
### Steps to reproduce
1. send commands to AWG
2. restart the console after error, when apparently the command is not executed
3. reinitialize AWG
4. send new command to AWG
5. result: mismatch between most resent send command and command being executed by the AWG

### Expected behaviour
Adapt the driver of the AWG in such a way that it clears the communication with the computer when it is initialized

### Actual behaviour
Keeps old commands in communication channel, causing confusion of what command is being executed

### System
**operating system** Windows 7

**qcodes branch** master

**qcodes commit** 83542518f422b18d2d4c31ad2d5655049164ef8a

@CumulonimbusCalvus

Start by locating the Tektronix5014C AWG driver and its initialization and communication entry points. Reproduce the listed sequence on the stated Qcodes commit, then verify that reinitialization clears pending communication so the next command is the one executed by the AWG.

Written by the indexing model from the issue text.