Config components unit test from scons refinement

Address review comments from https://review.opencontrail.org/#/c/3031
patchset 8 (SConscript having file dependencies instead
of directory and use links to find packages listed in requirements)

Change-Id: I8e34f347ce5f0c034a379f7e25370bcb8a64fa45
Merge "Config components unit test from scons refinement"