Do not print error string "unknown keyword in config: copylinkedpackages:"

Do not print error string "unknown keyword in config: copylinkedpackages:"

We add "CopyLinkedPackages: yes" in the project config
to reduce build redundancy for prerelease projects.
After then, "build" package complains
"unknown keyword in config: copylinkedpackages:"
because it does not understand this keyword
even though it does not need to understand this keyword.

Hence, I just added an "if" statement not to print this complain.

Change-Id: I5aa4044e629cf1f1a4af1318eb6b2ded8ac982fb
Signed-off-by: Junghyun Kim <jh0822.kim@samsung.com>