Fix aarch64 image naming in parser

Fix aarch64 image naming in parser

Some hardcoded values within the parser project create problems for
opnfv-armband. In this patch we fix image naming for parser, at
least for the testcase we run in opnfv-ci.

1)Tosca functions like get_attribute() or get_item() could in theory
be used but due to the current structure of the vRNC file it is not
possible.

JIRA: ARMBAND-369
JIRA: PARSER-175

Change-Id: I8cdc82b9e5c9008f3a3a5110d65706440d208ab8
Signed-off-by: Charalampos Kominos <Charalampos.Kominos@enea.com>