Exclude local path prefixes from being cached

[jjhursey]

• Feature enabled by default, but can be disabled by setting the
  envar SPINDLE_DISABLE_EXCLUDE=1

[jjhursey]

This one I would like to get some feedback on. I don't love the explicit list of file system mounts. Something better might be to check the file system associated with the path to exclude the local file system mounts. I wasn't sure how to do that portably / efficiently.
I'm mostly posting this for comment/discussion.

[mplegendre]

I like the feature, but agree about needing a better implementation. Some of those hardcoded paths are NFS on our linux clusters.

The last release added an internal capability to parse the system's mount points in the server:
https://github.com/hpc/Spindle/blob/devel/src/server/auditserver/parse_mounts.cc

We're currently using this to correct the device field in stat calls when different nodes have different device major/minor ids. But we could also parse a prefix list out of this that identifies local filesystems. Then have servers respond to clients with a message to self-read if it sees something prefixed as local.

We'd need a proper list of what filesystem types are remote vs local.

[mplegendre]

Closing old PRs. This got implemented as a configurable feature some time ago.