Use environment variable for image properties

Use environment variable for image properties

Use IMG_PROP environment variable to read extra image
properties.

Set image_extra_properties for scsi volume types
without file patch, but using IMG_PROP env variable
IMG_PROP is defined through releng.

Image extra_properties will continue to get updates from
functest config file

With this change, remove unnecessary parameters from arm patch
Related to:https://gerrit.opnfv.org/gerrit/#/c/63203/

JIRA:ARMBAND-402

Change-Id: I64139240751b1e109bbe24ba32f487ccd98b9a92
Signed-off-by: Delia Popescu <delia.popescu@enea.com>