Fix error in downloading hippomocks library.

Fix error in downloading hippomocks library.

Apparently, the filename of the hippomocks library zip file that is
downloaded from the github changed from 'master.zip'
to 'hippomocks-master.zip' since the hippomocks.scons script was created.

This modification uses a SHA hash to download a specific version of
the hippomocks library.

Change-Id: Iaa3b523b11c35a918a0a3de22876f2d62f339372
Signed-off-by: Doug Hudson <douglas.hudson@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/454
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Joseph Morrow <joseph.l.morrow@intel.com>
Reviewed-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>