Description of problem:
My setup uses a APC master switch (Specificly a RackPDU 7800.) to fence it's hosts. The APC unit configured for telnet access. The apc fence type is used by oVirt to handle this fencing type.

When /usr/bin/fence_apc is invoked by the user, the command succeeds. When the engine invokes the command, we see that the it has appended an extra string, (in this case a " -6"), to the open command given to the telnet binary. The extra string results in failure to fence the host. Although an IP address is used below, the same result occurs if the engine is given a DNS hostname.

---snip---
May 01 07:02:05 azura.codenet /fence_apc[18208]: Timeout exceeded.
                                                 <fencing.fspawn object at 0x7f6ffd503048>
                                                 command: /usr/bin/telnet
                                                 args: [b'/usr/bin/telnet']
                                                 buffer (last 100 chars): 'net> open 192.168.9.50 -6\r\ntelnet: 192.168.9.50: Address family for hostname not supported\r\nt>
                                                 before (last 100 chars): 'net> open 192.168.9.50 -6\r\ntelnet: 192.168.9.50: Address family for hostname not supported\r\nt>
                                                 after: <class 'pexpect.exceptions.TIMEOUT'>
                                                 match: None
                                                 match_index: None
                                                 exitstatus: None
                                                 flag_eof: False
                                                 pid: 18210
                                                 child_fd: 6
                                                 closed: False
                                                 timeout: 30
                                                 delimiter: <class 'pexpect.exceptions.EOF'>
                                                 logfile: None
                                                 logfile_read: None
                                                 logfile_send: None
                                                 maxread: 2000
                                                 ignorecase: False
                                                 searchwindowsize: None
                                                 delaybeforesend: 0.05
                                                 delayafterclose: 0.1
                                                 delayafterterminate: 0.1
                                                 searcher: searcher_re:
                                                     0: re.compile('(login\\s*: )|((?!Last )Login Name:  )|(username: )|(User Name :)')
May 01 07:02:05 azura.codenet /fence_apc[18208]: Unable to connect/login to fencing device

Version-Release number of selected component (if applicable):
ovirt-host-4.5.0-3.el8.x86_64
vdsm-4.50.0.13-1.el8.x86_64
fence-agents-apc-4.2.1-89.el8.noarch

How reproducible:
Always.

Steps to Reproduce:
1. Set up power management for a host in oVirt 4.5 to use the "apc" fence type, do not enable the secure option.

2. Attempt to fence the host. Or test the fence agent's configuration in the admin UI.

Actual results:
Failure to fence the host. Failure to get power management status. Test configuration fails.

Expected results:
Host can be fenced, power management status is retrievable, test configuration passes.

Additional info:
There seems to be a similar issue described in an old discussion on the oVirt users mailing list: https://lists.ovirt.org/archives/list/users@ovirt.org/thread/GBD7MUJKXDZE56TYUCBJNDE7TWS7CHTZ/