Implement timeouts for the Xrootd client.

[bbockelm]

The default timeout is now set to 10 minutes; previously, it varied
between 3 minutes and 8 hours, depending on the operation. Further,
the timeout can now be set by the CMSSW pset and the site local
config service.

It appears that timeouts were never set for fallback files;
this issue is now fixed.

Whenever a ReadV error occurs, raise a CMSSW exception; do not
allow this to be cast down to a ROOT warning. Exception information
is improved so the last Xrootd server message (or timeouts) are
recorded.

Finally, this fixes an older bug in XrdReadv.cc which causes the
transaction timeout to not be reset at the beginning of ReadV calls.
This causes the XrdAdaptor to throw an exception on ReadV
calls if it has been more than the timeout (default, 8 hours) between
Read calls (which did reset the transaction timeout).

This is a backport of PR #5714 per request from @davidlange6

[cmsbuild]

A new Pull Request was created by @bbockelm (Brian Bockelman) for CMSSW_6_2_X_SLHC.

Implement timeouts for the Xrootd client.

It involves the following packages:

IOPool/Input
Utilities/XrdAdaptor

@cmsbuild, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
@wddgit, @wmtan this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@fratnikov, @mark-grimes you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_6_2_X_SLHC IBs unless changes or unless it breaks tests. @fratnikov, @mark-grimes can you please take care of it?

[fratnikov]

merge