add test / fix for lpdot

[frrad]

Without the change to lpdot, this new test fails with

E       AssertionError: assert [{'name': 'x', 'value': 1}] == [{'name': 'x', 'value': 2}]
E         
E         At index 0 diff: {'name': 'x', 'value': 1} != {'name': 'x', 'value': 2}
E         Use -v to get more diff

The lpdot function uses isiterable to check for "vector" types, however an LpAffineExpression is iterable.

[CLAassistant]

All committers have signed the CLA.

[frrad]

I did a bit more looking around and found #572 and #483 for the same issue :-/

Just wanted to flag so that when you eventually take one of them you can close the other.

[frrad]

Thanks!