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
Merge tag 'pulp-nodes-2.5.1-0.2.beta' into 2.5-release

Tagging package [pulp-nodes] version [2.5.1-0.2.beta] in directory [nodes/].
Release 2.5.1
Automatic commit of package [pulp] release [2.5.1-1].
Automatic commit of package [pulp-nodes] release [2.5.1-1].
Merge branch '2.5-release' into 2.5-dev
Update the version in the spec files