rm creation of InstalledProductManager in reg cli

A InstalledProductManager was being created in the
__init__ for RegisterCommand, so all cli invocations
were creating at least one extra inst of
InstalledProductManager (which has EntitlementDirectory
and ProductDirectory) which was causing an extra
load/parse of all product and entitlement certs.
Merge pull request #647 from candlepin/alikins/remove_ipm_from_regcommand_init

rm creation of InstalledProductManager in reg cli