Delay load of package Meta
Delay load of package Meta

When MuranoPackage instance is created and it has
Meta referring to classes in the same package there
will be an exception because no classes were registered
in the package yet.

The solution is to have lazy metadata load upon first
call to get_meta()

Change-Id: I9a6cb96924e9d66fb79405763142bc78477940f1
Closes-Bug: #1557099

NeCTAR-RC/murano,DavidPurcell/murano_temp,openstack/murano,NeCTAR-RC/murano,DavidPurcell/murano_temp,openstack/murano,DavidPurcell/murano_temp,DavidPurcell/murano_temp,NeCTAR-RC/murano,NeCTAR-RC/murano