Coerce -p values for export/import cli to Integer

The -p option when used was throwing an assertion error, due to it being passed
to downstream functions as a string. This patch coerces these values to an
Integer at the clojure.tools.cli level.

Extra tests have been added to test setting -p and -H explicitly also.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #542 from kbarber/port_option_coerce_to_integer

Coerce -p values for export/import cli to Integer