Description of problem:
When ipa-server-install arguments --auto-reverse and --allow-zone-overlap are
used together, the reverse zone does not get created.

As the --auto-reverse logic is designed to not create a reverse zone if it
exists, I am unsure if the --allow-zone-overlap argument should supercede the
--auto-reverse behavior.

If the current behavior is intended then it would be nice to clarify the
expected result of using these two options together in the man page(in that
case please consider this BZ as only a man page change).

Version-Release number of selected component (if applicable):
RHEL 7.4
ipa-server 4.5

How reproducible:
Always

Steps to Reproduce:
1. Create existing reverse zone, or point to DNS server with an already
existing reverse zone
2. run 'ipa-server-install' with --auto-reverse and --allow-zone-overlap
arguments
3.

Actual results:
--allow-zone-overlap is ignored

Expected results:
Have --allow-zone-overlap create the reverse zone anyway.