Disable plymouth to workaround not reaching sysinit.target

Resolves: rhbz#1060789
Handle missing version arguments

Workaround the different handling of missing arguments between argparse
and optparse.

Resolves: rhbz#1069836
Require --instrepo with --network.

RHEL has no default mirrorlist and upgrades through CDN are not yet
supported, so require that --network specifies where that is.

Resolves: rhbz#1070080
Fix the reboot command for RHEL 6.

systemctl? That's not gonna work.

Resolves: rhbz#1070821
New version 0.7.9