Added build directory to .gitignore. Without this, recent sonar scans
are including generated source files under build/lib as uncovered
source, which is not correct.
Change-Id: Ic24a438313bc09271d306c7eff97aab8e083efca
Issue-ID: CCSDK-2354 Signed-off-by: Dan Timoney <dtimoney@att.com>