Description of problem:

DASD disks are limited to 3 partitions. When trying to create a fourth partition, the installer complains and print "Failed to add new device. Click for details".

When clicking for details, an empty box is printed, which doesn't help much the admin understand what is going on.

See screenshots for details:

• layout.png
• click_for_details.png

Version-Release number of selected component (if applicable):

RHEL 8.1 DVD

How reproducible:

Always

Steps to Reproduce:
1. Format a DASD device with more than 3 partitions.

Expected results:

Dialog shows "No free partition slots on dasda" or similar.

Additional infos:

storage.log excerpt:
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
19:07:32,813 DBG storage.ui: checking freespace on dasda
19:07:32,813 DBG storage.ui: size 1024 KiB rounded up to 1 MiB for disk dasda
19:07:32,813 DBG storage.ui: no free partition slots on dasda
19:07:32,815 ERR storage.ui: failed to allocate partitions: Unable to allocate requested partition scheme.
19:07:32,815 ERR storage.ui: device post-create method failed: Unable to allocate requested partition scheme.
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------