Add check for Read-Write images support (#965)

* Fix enqueue_flags test to use correct barrier type.

Currently, enqueue_flags test uses CLK_LOCAL_MEM_FENCE.
Use CLK_GLOBAL_MEM_FENCE instead as all threads across work-groups
need to wait here.

* Add check for support for Read-Wrie images

Read-Write images have required OpenCL 2.x.
Read-Write image tests are already being skipped
for 1.x devices.
With OpenCL 3.0, read-write images being optional,
the tests should be run or skipped
depending on the implementation support.

Add a check to decide if Read-Write images are
supported or required to be supported depending
on OpenCL version and decide if the tests should
be run on skipped.

Fixes issue #894

* Fix formatting in case of Read-Write image checks.

Fix formatting in case of Read-write image checks.
Also, combine two ifs into one in case of
kerne_read_write tests

* Fix some more formatting for RW-image checks

Remove unnecessary spaces at various places.
Also, fix lengthy lines.

test_common/harness/kernelHelpers.h

@@ -141,6 +141,7 @@ extern test_status verifyImageSupport( cl_device_id device );
 /* Checks that the given device supports images. Same as verify, but doesn't print an error */
 extern int checkForImageSupport( cl_device_id device );
 extern int checkFor3DImageSupport( cl_device_id device );
+extern int checkForReadWriteImageSupport(cl_device_id device);
 
 /* Checks that a given queue property is supported on the specified device. Returns 1 if supported, 0 if not or an error. */
 extern int checkDeviceForQueueSupport( cl_device_id device, cl_command_queue_properties prop );