Refactor selecting values from an attribute

Move the code to select particular keys/indices from an attribute value out
of the get_attr intrinsic functions and into the attributes module as a
separate function.

Change-Id: I16135159027cc52e8da74a4b5863fc8a8595d582
Convert AWS::EC2::Subnet to use attributes Schema

Change-Id: I0f7b6beef1023875ae499ce7ec06f4211c6c028b
Remove rst2script.sed and integration.sh

rst2script.sed was referenced in the Fedora getting started
documentation, but the recommended way to use Heat/Openstack
on Fedora is now to use RDO/packstack.

Also removes the reference to rst2script.sed in the
getting_started/on_fedora documentation.

Also removes obsolete integration.sh script.

Partial-Bug: 1338066

Change-Id: I7f2b0d84ccef324ccb8e32ca4c6d90f9a3f2dda3
Merge "Refactor selecting values from an attribute"
Merge "Convert AWS::EC2::Subnet to use attributes Schema"
Merge "Remove rst2script.sed and integration.sh"