Use rspec -P pattern option in rake tasks

rspec has an internal option (-P) to receive pattern of files to run via the command line, use this option in rake_tasks instead of passing through a huge list of files one by one on the command line.
Also, the pattern we use for `rspec` (w/o rake) is `'**/*_spec.rb'`.  Seems like they should be the same.  We may need to do some git history spelunking to find out why they diverged and figure out which is the correct one.