webadmin: Show only compatible OSes

This change modifies the frontend to show only OSes compatible with the
architecture of the VM or pool being created.

Change-Id: I19f5a2fa8ca6a54e75f4ff64c4b6189db13ed25d
Signed-off-by: Leonardo Bianconi <leonardo.bianconi@eldorado.org.br>
Signed-off-by: Gustavo Pedrosa <gustavo.pedrosa@eldorado.org.br>
Signed-off-by: Vitor de Lima <vitor.lima@eldorado.org.br>