Fix the handling of task args

The args were all being read, which caused problems when values
passed didn't read to the expected type (eg. strings containing a
single / were read as symbols). It is now the task's responsibility
to do any reading required. Fixes #161.
Rename test-resouces to dev-resources

Aligns with lein 2 usage
Fix processing of groups in converge

Groups specified as a sequence with :count keys were being ignored.
Add pallet.api/print-targets

Add a function to print the targets of an operation in a table.
Only add a dash in cluster-spec if prefix given

If a cluster-spec is requested with a blank prefix, do not add a dash to the
group names.