fence_zvmip: Update longdesc to document all required functions

In RHBZ#1935641, IBM explained that the requesting user needs
authorization for more functions than what is currently documented.

They said:
"""
What we found is that you need rights from three different NICKS:
SERVER_MANAGEMENT, IMAGE_CHARACTERISTICS and IMAGE_OPERATIONS.
You won't be able to give a user all three NICKS.
Therefore, you have to create a new NICK with all capabilities from all
three NICKS together and then assign the new NICK to the USER
"ZCLUSTER".
Even better is to just use the needed Subset with a new NICK.
We found five commands which are used in the fencing code and on the
z/VM Log which should be enough for fencing to work.

We suggest creating following files:

File VSMWORK1 NAMELIST:

:nick.ZVM_FENCE
:list.
IMAGE_ACTIVATE
IMAGE_DEACTIVATE
IMAGE_STATUS_QUERY
CHECK_AUTHENTICATION
IMAGE_NAME_QUERY_DM

File VSMWORK1 AUTHLIST:

ZCLUSTER                            ALL                              ZVM_FENCE

For details, we suggest adding a link to the current z/VM docu:

• NAMELIST: https://www.ibm.com/support/knowledgecenter/de/SSB27U_7.2.0/com.ibm.zvm.v720.dmse6/namelst.htm
• AUTHLIST: https://www.ibm.com/support/knowledgecenter/de/SSB27U_7.2.0/com.ibm.zvm.v720.dmse6/auf.htm

"""

Resolves: RHBZ1935641

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>