Fix spelling miss of password_func variable

In novaclient/shell.py there is a variable called 'password_fun'
which isn't used anywhere.
In fact it's a spelling miss, and should be modified to 'password_func'
which is used in novaclient/client.py
This patch fixes this bug.

Change-Id: Ibb8e95a2efc77575dcc8544584c708c5c62b7dea
Merge "Fix spelling miss of password_func variable"