Create utf unit tests for build_component.py.

[XuefengHuang]

I add some unit tests to check if these functions work fine and results are correct in build_component.py. I add cloning and copying of seattlelib_v2 repo because I need extra files to test process_mix() function.
I have tested them on Mac OS X system. There is my test result:

172-16-21-124:~ Xuefeng$ git clone https://github.com/XuefengHuang/common -b unittests
fatal: destination path 'common' already exists and is not an empty directory.
172-16-21-124:~ Xuefeng$ git clone https://github.com/XuefengHuang/common -b unittests
Cloning into 'common'...
remote: Counting objects: 252, done.
remote: Compressing objects: 100% (146/146), done.
remote: Total 252 (delta 123), reused 206 (delta 98)
Receiving objects: 100% (252/252), 64.47 KiB | 0 bytes/s, done.
Resolving deltas: 100% (123/123), done.
Checking connectivity... done.
172-16-21-124:~ Xuefeng$ cd common/scripts
172-16-21-124:scripts Xuefeng$ python initialize.py
Checking out repo from https://github.com/SeattleTestbed/common ...
Done!
Checking out repo from https://github.com/SeattleTestbed/utf ...
Done!
Checking out repo from https://github.com/SeattleTestbed/seattlelib_v2 ...
Done!
172-16-21-124:scripts Xuefeng$ python build.py -t
Building into /Users/huangxuefeng/common/RUNNABLE
Done building!
172-16-21-124:scripts Xuefeng$ cd ../runnable
172-16-21-124:runnable Xuefeng$ python utf.py -a
Testing module: common
    Running: ut_common_copyfilessubdir.py                       [ PASS ]
    Running: ut_common_copytotarget.py                          [ PASS ]
    Running: ut_common_copytreetotarget.py                      [ PASS ]
    Running: ut_common_helpexit.py                              [ PASS ]
    Running: ut_common_processmix.py                            [ PASS ]
    Running: ut_common_replacestring.py                         [ PASS ]
    Running: ut_common_test_file.py                             [ PASS ]

[aaaaalbert]

I suggest to refactor this to

• Build a dummy component specific to this unit test,
• which has a separate build config,
• and instead of re-reading the build config, compare the resulting file list after building with a hardcoded file list.

This avoids testing the correctness of a function (reading in the build config in this case) using the same function (i.e. the code below this comment, copied in from build_component.py)