userportal,webadmin: vm name max length validation hardcoded

There is a config value MaxVmNameLengthWindows and MaxVmNameLengthNonWindows
for VM name lengths, but the frontend ignored this config values and had
the lenghts hardcoded.

Change-Id: I08eae6dac69963f7c604cf80bba423f0987a199c
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>