Use clFinish to gurantee commands completed, instead of waiting for events.
Signed-off-by: NWu Zhiwen <zhiwen.wu@intel.com>

no changes in code

The same code was repeated several time for different data types, so
it was extracted as a templated function to improve maintability and
make a code more clear.

Exception may be rasied inside the body of a copying constructor after
refcount has been increased, and beacause in the case of the exception
destrcutor is never called what causes memory leak. This commit adds a
workaround that calls the release() function before the exception is
thrown outside the contructor.