[Coverage/Fix] Disable optimization and remove redundant gcov run

[Coverage/Fix] Disable optimization and remove redundant gcov run

This patch disables code optimization for coverage analysis and remove
redundant gcov run.

In fact, we don't need to run the python script, unittestcoverage.py
which recursively executes gcov. Because lcov internally execute gcov,
the results of the script are never used.

FYI...
- when program is compiled with coverage option, .gcno files are created.
- When such programs are executed, .gcda files are created.
- As lcov input files are .gcda. we don't need to run gcov before lcov.

Signed-off-by: Dongju Chae <dongju.chae@samsung.com>