Correct autodetection of bootfs property

Remove lines that contain only a hyphen (match '^-$' instead of '-').

I had a root fs with a hyphen in the name (fedora/ROOT/Fedora20-Dev),
it was not detected because sed eliminated that line of output from
'zpool list -Ho bootfs'.

Signed-off-by: Evan Susarret <evansus@gmail.com>
Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2196

(cherry picked from commit dc55d791011b31317ad57ecb36be0a27b7647ef2)
Re-enable zfs-dracut packaging

This was disabled with f044301bacbe69848fd4c0fcd02f5b4d08d7f298
in January 2012 as it was broken back then, but the situation
has improved vastly in the meantime. The zfs-dracut package
not only works well with dracut-038 on Debian Jessie but offers
one significant advantage over initramfs-tools: The ability to
export a ZFS root on shutdown, eliminating the necessity to
force-import on every reboot.