[libvirt] Add patches to allow users to join running containers.

[dwalsh at redhat.com]

[PATCH 1/2] Add virGetUserDirectoryByUID to retrieve users homedir
[PATCH 2/2] virt-login-shell joins users into lxc container.

This patch implements most of the changes suggested by Dan Berrange and 
Eric Blake.

Some replies to suggested changes.

Removed mingw-libvirt.spec.in changes since virt lxc probably can not be 
supported in Windows.  Not sure if I need to make changes so my code will not 
build on that platform.

Did not make the changes to install virt-login-shell as 4755 automatically.
I guess I want a more firm, make that change request...

I did not make a helper function to parse a list of strings out of conf file.

The getuid and getgid calls return the user that executed the program, when the app is setuid geteuid and getegid return "0".  I believe getuid and getgid are correct.

Added virt-login-shell --help, not sure what --program would do?

The program is hard coded to LXC because there is no way that I know of for a ZZ
process to join a running qemu instance.

I have heard back from one security review from Miloslav Trmac, who had similar comments as Eric.