v2v: Fix --help documentation of -o glance option.

Thanks: Junqin Zhou
v2v: If non-Xen and Xen initrds match a kernel, take shortest name (RHBZ#1141145).

Thanks: Tingting Zheng.
sysprep: Replace --user-accounts option with --{remove,keep}-user-accounts.

The --user-accounts option, with its double-negative '-' prefix on
user names, is confusing.  Replace it with '--remove-user-accounts'
and '--keep-user-accounts' options.

This updates commit 128d474095bfabc2d724d0181155e364f1afbabf.
sysprep: Add an optional method for checking if unused arguments were passed to disabled operations.
sysprep: Check --{keep,remove}-user-accounts parameters are not used when operation is disabled (RHBZ#1141157).

You will see an error like this:

$ virt-sysprep --remove-user-accounts foo,bar -a /dev/null
virt-sysprep: error: user-accounts: --remove-user-accounts parameter was
used, but the "user-account" operation is not enabled
v2v: -i libvirtxml: Give an error if local disks are not readable (RHBZ#1140946).
v2v: Add -o null mode.

In theory this discards the output.  Unfortunately in practice we have
to write the output to a temporary file and delete it (because of
limitations in qemu-img convert).
v2v: esx: Clarify that username can be specified in vpx:// URI (RHBZ#1141113).

If there is an authentication error when getting the session cookie,
emphasize in the error message that the username can be specified in
the URI.

Unfortunately libvirt asks for the username previously, but we cannot
access that.
sysprep: Ensure error handler surrounds all the code so we catch and print all errors.
sysprep: Use 'error' function consistently throughout the program.
Version 1.27.44.
RHEL 7: Emphasize libguestfs-winsupport package (RHBZ#627468).

This RHEL-only patch changes the error messages when the
inspection code cannot find an operating system inside the guest
image.  For a Windows guest this may happen because the user has not
installed the separate 'libguestfs-winsupport' package.  Therefore we
emphasize that the user may need to install this package.

Notes:

(1) In RHEL there are two pieces of inspection code, the old Perl code
(deprecated upstream) and the new C core inspection API.  Therefore
this patch has to touch two places with essentially the same change.

(2) This patch doesn't try to be clever and detect if it was a Windows
guest.  This should reduce the chance of failure.

Output from (Perl) virt-inspector now looks like this:

 $ virt-inspector disk.img
 No operating system could be detected inside this disk image.

 This may be because the file is not a disk image, or is not a virtual machine
 image, or because the OS type is not understood by virt-inspector.

 If you feel this is an error, please file a bug report including as much
 information about the disk image as possible.

 RHEL notice
 -------------
 libguestfs will return this error for Microsoft Windows guests if the
 separate 'libguestfs-winsupport' package is not installed. If the
 guest is running Microsoft Windows, please try again after installing
 'libguestfs-winsupport'.

Output from guestfish (ie. C core inspection API) now looks like this:

 $ guestfish -i disk.img
 guestfish: no operating system was found on this disk

 RHEL notice
 -------------
 libguestfs will return this error for Microsoft Windows guests if the
 separate 'libguestfs-winsupport' package is not installed. If the
 guest is running Microsoft Windows, please try again after installing
 'libguestfs-winsupport'.
RHEL 7: Remove libguestfs live (RHBZ#798980).

This isn't supported in RHEL 7.
RHEL 7: Remove 9p APIs from RHEL (RHBZ#921710).
RHEL 7: Disable unsupported remote drive protocols (RHBZ#962113).

This disables support for unsupported remote drive protocols:

 * ftp
 * ftps
 * http
 * https
 * tftp
 * gluster
 * iscsi
 * rbd
 * sheepdog
 * ssh

Note 'nbd' is not disabled, and of course 'file' works.

We hope to gradually add some of these back over the lifetime of RHEL 7.