update keithley client

Update the Keithley DMM client so that it saves the voltage measurement of BNC526 and BNC 529 in separate file.
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
add feature to record the time passed (in minutes)
Update keithley_client.py
Record the time passed in minutes
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update keithley_client.py
Update voltage_conversion.py
Update keithley_client.py