libxcmd: check CMD_FLAG_GLOBAL inside args_command()

libxcmd: check CMD_FLAG_GLOBAL inside args_command()

Rather than having multiple methods of executing commands from the
CLI, use CMD_FLAG_GLOBAL to indicate a one-shot command rather than
an iterative command from args_command(). This simplifies the main
loop processing.

To make it more obvious what this CMD_FLAG_GLOBAL flag does, rename
it to CMD_FLAG_ONESHOT to indicate that the command should only ever
be executed once and not iterated.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>