Log errors when invoking a subcommand

The main dispatcher scans available namespaces and dispatches to the
specified "-main" function. For example, running the "services"
subcommand would trigger loading of the "-main" function in the
"com.puppetlabs.puppetdb.cli.services" namespace.

However, if there was an error during the attempt to "require" that
namespace, it wouldn't be logged properly. This commit adds the
"require" step to the existing try/catch block.
Fix broken require
Merge branch 'namespace-fix' into 1.5.x

* namespace-fix:
  Fix broken require
  Log errors when invoking a subcommand