tools: Bump library SONAMEs for 4.4

tools: Bump library SONAMEs for 4.4

There have been ABI/API changes in libxc.  Bump its MAJOR (which
affets libxenguest et al too.)

There have been ABI changes in libxl.  Bump its MAJOR.
(The API changes have been dealt with as we go along - there is
already a LIBXL_API_VERSION 0x040400.)

None of the other libraries have changed their interfaces.  I have
verified this by building the tools and searching the dist/install
tree for files matching *.so.*.  For each library that showed up, I
did this:
  git-diff RELEASE-4.3.0..staging -- `find tools/FOO/ -name \*.h`
where FOO is the corresponding source directory.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>