fallback to hostname in scripts/package/builddeb

fallback to hostname in scripts/package/builddeb

I happened to build a kernel with "make deb-pkg" on a machine with no
network connectivity, but this failed with:

[...]
  INSTALL debian/headertmp/usr/include/asm/ (65 files)
hostname: Name or service not known
../scripts/package/Makefile:90: recipe for target 'deb-pkg' failed
make[2]: *** [deb-pkg] Error 1

In scripts/package/builddeb it tries to construct an email address (that
can be queried in /proc/version later on) but with no network,
the "hostname -f" fails. The following patch falls back to just use the
shortname if we cannot determine our FQDN.

Signed-off-by: Christian Kujau <lists@nerdbynature.de>
Signed-off-by: Michal Marek <mmarek@suse.cz>