Test coverage for NFS/Kerberos

[chucklever]

The areas we are typically concerned about are performance, interoperability (spec compliance), and stability. So far we have little or no testing of Kerberos; in particular:

• whether Kerberos properly rejects unauthenticated and unauthorized requests
• how much performance and scalability are impacted
• how stable and reliable it is to run with Kerberos enabled

It's difficult to automate Kerberos testing because a KDC is necessary (could be on the NFS server host, but still needs to be configured) and keytabs need to be provisioned and distributed to all test hosts.

[chucklever]

Scott Mayhew constructed and committed support in kdevops for the use of Kerberos during fstests runs.