(#19514)(PP-773) Rename hashed_node_data and cliencert for $trusted

This renames hashed_node_data to trusted_node_data, and
the element 'clientcert' to 'certname'.

This also fixes the issues regarding immutability reported in PP-773.
It is now not possible to alter the trusted data. (A freeze was missing
when the data was created). As extra precaution, the data is frozen when
set as trusted data in the node.

There is now also a warning if an attempt is made to modify the trusted
data by manipulating a node.
(#19514) Correct error message matching for Ruby 1.8.7

In Ruby 1.8.7, the error message for an attempt of mutating
a frozen hash refers to 'hash' using lower case whereas later versions
use capital 'H'. This caused two tests to fail (twice).
Merge pull request #2084 from hlindberg/issues/issue-19514

(#19514)(PP-773) Rename hashed_node_data and cliencert for $trusted
(maint) Remove misleading comment regarding msExtReq

Puppet has never provided a way to add microsoft extension requests to
generated CSRs, so it's not something we would necessarily restore. This
commit removes a comment that indicates that we used to support
msExtReq.
(#23201) Allow CSRs to return multiple extension requests
(#23201) Extract CSR extension_request attr generation
(#23201) allow custom fields to be added to CSR extReq
(#23201) don't assign OIDs when looking up extension requests

The `Puppet::SSL::CertificateRquest#subject_alt_names` method was trying to
select all of the subjectAltName extensions in the extension requests,
but was accidentally assigning that OID to all extensions instead of
comparing them.

Before 63cecc56 subjectAltName was the only possible extension request so
this was innocuous, but following that commit this error was destructive.
This commit resolves the issue by using the comparison operator instead
of assignment.