ca-certificates: fix installation for target.

Target installation step should be appended rather than overriding
the whole installation step otherwise this would fail for target
installations becuase the corresponding files are not available.

Signed-off-by: Awais Belal <awais_belal@mentor.com>
Merge pull request #22 from abelal/ca-certificates-fix-installation

ca-certificates: fix installation for target.