docs,rng: Adjust storage pool name grammar checks

docs,rng: Adjust storage pool name grammar checks

https://bugzilla.redhat.com/show_bug.cgi?id=1475250

It's possible to define and start a pool with a '.' in the
name; however, when trying to add a volume to a domain using
the storage pool source with a '.' in the storage pool name,
the domain RNG validation fails because RNG uses 'genericName'
which does not allow a '.' in the name.

Domain XML def parsing has a virXMLValidateAgainstSchema which
generates the error. The Storage Pool XML def parsing has no
call to virXMLValidateAgainstSchema. The only Storage Pool name
validation occurs in virStoragePoolDefParseXML to ensure the
name doesn't have a '/' in it and in storagePoolDefineXML to
call virXMLCheckIllegalChars using the same parameter "\n" as
qemuDomainDefineXMLFlags would check after the RNG check
could be succesful.

In order to resolve this, create a poolName definition in
storagecommon.rng that will mimic the domain name regex that
disallows a newline character, but add the "/" in the exclude
list. Then modify the pool and volume source name definitions
to key off that poolName.