Add two functions to enable manual addition of ECKD DASDs.

This just adds a couple of functions which aid in manually adding DASDs.
sanitize_dasd_dev_input takes a device number as a string and verifies
whether its format is acceptable as a match against DASD device numbers.

online_dasd takes a device number as a string and fill remove the device
from the ignore list and attempt to bring it online.
Add a test file for DASD handling (#1070115)

Related: rhbz#1070115

Signed-off-by: mulhern <amulhern@redhat.com>
Condense and comment some devicelibs.dasd methods (#1070115)

Related: rhbz#1070115

Signed-off-by: mulhern <amulhern@redhat.com>
Change the default /boot part on s390x to not be lvm.

Avoid any insidious problems that may result from having /boot on lvm
on s390x, and simply change the default partitioning for /boot to be
on a partition.
Remove all traces of singlePV.

Won't be needing this anymore.
Remove a problematic remnant of singlePV.

commit e4549cfd0c794c4b0cf139fb3002885c88315788 removed only part of
a conditional clause that should have been removed completely. The result
was that all actions that create LVs within a given VG required each
other, leading to cycles in the tsort input graph.

Resolves: rhbz#1147985