1022198: Display highest suggested quantity in contract selection

We group similar pools together in the gui.  Because we only
match similar pools, it doesn't matter which pool we read
attributes from.  However the suggested quantity is based
upon the available quantity, which varries by pool, so
we should display the highest number.
Fix failing test when no products are installed
Merge pull request #812 from candlepin/ckozak/merged_default_quantity

Ckozak/merged default quantity