Support files removed for CONF.scenario.img_dir option

CONF.scenario.img_dir file has been removed along with any other
support files. Exception has been raised when a user passes an
img file that does not exist in the CONF.scenario.img_file.
Exceptions import has been added for lib_exc.

Closes-Bug: #2032948
Change-Id: I2b57dd4928ab3f6858909fc90b7865aac2d93da2
1 file changed