Delay import of psutil to avoid AVC

Commit cfad7af35d added a check to ensure a
system has sufficient amount of memory. The feature uses psutil to get
available memory. On import psutil opens files in /proc which can result in
an SELinux violations and Python exception.

     PermissionError: [Errno 13] Permission denied: '/proc/stat'

Fixes: https://pagure.io/freeipa/issue/8512
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipaserver/setup.py

@@ -59,6 +59,7 @@ if __name__ == '__main__':
             "jwcrypto",
             "lxml",
             "netaddr",
+            "psutil",
             "pyasn1",
             "requests",
             "six",