Force test install to use innodb.

Fixes #5038

Props r-a-y

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7187 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
In BP_UnitTestCase::create_user(), default to last_activity one year ago

Setting the default last_activity in the past ensures that queries related to
most recently active/online users will not be disrupted by the accidental
creation of new users.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7188 cdf35c40-ae34-48e0-9cc9-0c9da1808c22