Switch to using c3.large testing instances

This switches us over to the newer c3.large instance types in EC2. After some
testing I've found these boxes are much faster and can complete our tests at
a faster rate. Not only that for pricing they are priced at $0.105 versus
$0.130 (c1.medium) per instance hour.

And since c1.medium are now in the 'previous generation' bucket, best to switch
away anyway.

Signed-off-by: Ken Barber <ken@bob.sh>
(PDB-900) Make performance improvements to fact_values GC process

Switched from a background thread to cleanup orphaned fact_values to one
that deletes as it goes. Switching to deferred constraints also
significantly improved performance on PostgreSQL. The same facilities are
not available in HSQLDB, but I have alternate queries that work, though
will likely not be as fast.
Mention that a -contrib package is required when install pg_trgm

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #1092 from kbarber/maint/stable/switch-to-c3-large-instances

Switch to using c3.large testing instances
Merge pull request #1096 from kbarber/maint/stable/mention-postgresql-contrib

Mention that a -contrib package is required when install pg_trgm
Merge pull request #1094 from senior/ticket/stable/pdb-900-fact-value-cleanup

(PDB-900) Make performance improvements to fact_values GC process
(PDB-13) Add wheezy to PDB acceptance tests

This PR adds a wheezy image to our acceptance tests.