build: Rename spec files to match the packages they produce

A spec file's name should match the base name of the packages it
produces.   This makes it easier to find the spec file given an
RPM, and to write generic makefile rules.

See https://fedoraproject.org/wiki/Packaging:NamingGuidelines?rd=Packaging/NamingGuidelines#Spec_file_name

Signed-off-by: Euan Harris <euan.harris@citrix.com>