We can't use GNULIB's fprintf-posix due to licensing
incompatibilities. We do already have a portable
formatting via virAsprintf() which we got from GNULIB
though. We can use to create a virFilePrintf() function.

But really gnulib could just provide a 'fprintf'
module, that depended on just its 'asprintf' module.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

On RHEL 6.4 (gcc 4.4.7), I got:

fdstreamtest.c: In function 'testFDStreamReadCommon':
fdstreamtest.c:44: error: declaration of 'tmpfile' shadows a global declaration [-Wshadow]

* tests/fdstreamtest.c (testFDStreamReadCommon)
(testFDStreamWriteCommon): Rename 'tmpfile' variable.
Signed-off-by: NEric Blake <eblake@redhat.com>

Add a test case which exercises the virFDStreamOpenFile
and virFDStreamCreateFile methods. Ensure that both the
synchronous and non-blocking iohelper code paths work.
This validates the regression recently fixed which
broke reading in non-blocking mode
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>