server install: fix KRA agent PEM file not being created
In commit 822e1bc82af3a6c1556546c4fbe96eeafad45762 the call to create the
KRA agent PEM file was accidentally removed from the server installer.
Call into the KRA installer from the server installer to create the file
again.
https://fedorahosted.org/freeipa/ticket/6392
Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>