Related-bug: #1413919 Related-bug: #1413923
Related-bug: #1413919
Related-bug: #1413923

Modified select2 to set the bottom instead of setting top in case of drop-down popup shown above the drop-down.
Setting top won't work in all cases especially if drop-down height is not constant like having collapse/expand containers within it.

Change-Id: I28feeca5c2d53e6804c85fff188eac21e58851e7

biswajit-mandal/contrail-webui-third-party,varunarya10/contrail-webui-third-party,JioCloud/contrail-webui-third-party,absingla/contrail-webui-third-party