The result of openfile was not checked, leading to failure deep in the
actual command with confusing error message, and exiting with exit code 0.

Here is a simple example - trying to read with the wrong format:

    $ touch file
    $ qemu-io -f qcow2 -c 'read -P 1 0 1024' file; echo $?
    can't open device file: Image is not in qcow2 format
    no file open, try 'help open'
    0

With this patch, we fail earlier with exit code 1:

    $ ./qemu-io -f qcow2 -c 'read -P 1 0 1024' file; echo $?
    can't open device file: Image is not in qcow2 format
    1

Failing earlier, we don't log this error now:

    no file open, try 'help open'

But some tests expected it; the line was removed from the test output.
Signed-off-by: NNir Soffer <nirsof@gmail.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-id: 20170201003120.23378-2-nirsof@gmail.com
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>