Update 2.5.x.rst

Add upgrade instructions:
 - run pulp-manage-db script
 - restart pulp services and httpd
Merge pull request #1411 from VuokkoVuorinnen/patch-1

Update 2.5.x.rst
1166202 - documenting that EPEL requires RHEL "optional" and "extras" repos
Merge remote-tracking branch 'origin/1166202'