Increase line coverage using LCOV_EXCL_LINE
and a pair of LCOV_EXCL_START and LCOV_EXCL_STOP in error handling code and
internal API function.
Policy to user LCOV_EXCL
1. Exclude error handling code from line coverage except invalid parameter.
2. Exclude entire internal API function using LCOV_EXCL_START and LCOV_EXCL_STOP.
Change-Id: I5fad3b2ccc311d8abf211e245cf0dae834f0515c
Signed-off-by: Unsung Lee <unsung.lee@samsung.com>